FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,             
                Plaintiff-Appellee,         No. 05-50410
               v.                            D.C. No.
MARK STEPHEN FORRESTER,                   CR-01-03177-TJW
             Defendant-Appellant.
                                      

UNITED STATES OF AMERICA,                  No. 05-50493
                Plaintiff-Appellee,           D.C. No.
               v.                          CR-01-03177-1-
DENNIS LOUIS ALBA,                              TJW
             Defendant-Appellant.              ORDER
                                             AMENDING
                                          OPINION AND
                                              DENYING
                                           PETITION FOR
                                          REHEARING AND
                                            SUGGESTION
                                          FOR REHEARING
                                           EN BANC AND
                                             AMENDED
                                             OPINION

       Appeal from the United States District Court
         for the Southern District of California
       Thomas J. Whelan, District Judge, Presiding

                  Argued and Submitted
          January 12, 2007—Pasadena, California


                            141
142               UNITED STATES v. FORRESTER
                    Filed July 6, 2007
                 Amended July 25, 2007
            Second Amendment January 7, 2008

      Before: Raymond C. Fisher, Richard R. Clifton and
              Milan D. Smith, Jr., Circuit Judges.

                  Opinion by Judge Fisher
                  UNITED STATES v. FORRESTER                145
                         COUNSEL

Benjamin L. Coleman, Coleman & Balogh LLP, San Diego,
California, for defendant-appellant Forrester.

Michael L. Crowley, San Diego, California, for defendant-
appellant Alba.

Todd W. Robinson, Assistant United States Attorney, San
Diego, California, for the plaintiff-appellee.


                           ORDER

  The amended opinion filed July 25, 2007, at slip opinion
9045-9066, 

(9th Cir. 2007), is amended as fol-
lows:

   At slip op. 9059, second full paragraph, line 5: change the
sentence beginning “We conclude that these surveillance
techniques are constitutionally indistinguishable . . .” to “We
conclude that the surveillance techniques the government
employed here are constitutionally indistinguishable . . .”.

   At slip op. 9060, continuation paragraph, line 8: change the
last two sentences in their entirety, beginning with “Analo-
gously . . .” and ending with “ . . . 

to “Analo-
gously, e-mail and Internet users have no expectation of
privacy in the to/from addresses of their messages or the IP
addresses of the websites they visit because they should know
that this information is provided to and used by Internet ser-
vice providers for the specific purpose of directing the routing
of information. Like telephone numbers, which provide
instructions to the “switching equipment that processed those
numbers,” e-mail to/from addresses and IP addresses are not
merely passively conveyed through third party equipment, but
rather are voluntarily turned over in order to direct the third
party’s servers. 

.
146                   UNITED STATES v. FORRESTER
   At slip op. 9060, first full paragraph: change the paragraph
beginning with “Second, e-mail to/from addresses . . .” and
ending at slip op. 9061 with “ . . . enable only the discovery
of addressing information.6” to: “Second, e-mail to/from
addresses and IP addresses constitute addressing information
and do not necessarily reveal any more about the underlying
contents of communication than do phone numbers. When the
government obtains the to/from addresses of a person’s e-
mails or the IP addresses of websites visited, it does not find
out the contents of the messages or know the particular pages
on the websites the person viewed. At best, the government
may make educated guesses about what was said in the mes-
sages or viewed on the websites based on its knowledge of the
e-mail to/from addresses and IP addresses — but this is no
different from speculation about the contents of a phone con-
versation on the basis of the identity of the person or entity
that was dialed. Like IP addresses, certain phone numbers
may strongly indicate the underlying contents of the commu-
nication; for example, the government would know that a per-
son who dialed the phone number of a chemicals company or
a gun shop was likely seeking information about chemicals or
firearms. Further, when an individual dials a pre-recorded
information or subject-specific line, such as sports scores, lot-
tery results or phone sex lines, the phone number may even
show that the caller had access to specific content informa-
tion. Nonetheless, the Court in Smith and Katz drew a clear
line between unprotected addressing information and pro-
tected content information that the government did not cross
here.6”.
  6
    Surveillance techniques that enable the government to determine not
only the IP addresses that a person accesses but also the uniform resource
locators (“URL”) of the pages visited might be more constitutionally prob-
lematic. A URL, unlike an IP address, identifies the particular document
within a website that a person views and thus reveals much more informa-
tion about the person’s Internet activity. For instance, a surveillance tech-
nique that captures IP addresses would show only that a person visited the
New York Times’ website at http://www.nytimes.com, whereas a tech-
                    UNITED STATES v. FORRESTER                      147
   At slip op. 9065, second full paragraph, line 6: change the
sentence beginning “We also hold that the government’s mon-
itoring . . . Fourth Amendment purposes and that, . . .” to “We
also hold that the techniques the government used to monitor
Alba’s e-mail and Internet activity did not constitute a search
for Fourth Amendment purposes and that, . . .”.

  The mandate shall issue immediately in United States v.
Forrester, No. 05-50410.

   The parties in United States v. Alba, No. 05-50493, may
file a petition for rehearing based on the amended opinion.

   With these amendments the panel has voted to deny Appel-
lant Alba’s petition for rehearing and suggestion for rehearing
en banc.

  The full court has been advised of the suggestion for
rehearing en banc and no judge has requested a vote on
whether to rehear the matter en banc. Fed. R. App. P. 35.

  Appellant Alba’s petition for rehearing and suggestion for
rehearing en banc, filed August 21, 2007, is DENIED.


                              OPINION

FISHER, Circuit Judge:

  Defendants-appellants Mark Stephen Forrester and Dennis
Louis Alba were charged with various offenses relating to the

nique that captures URLs would also divulge the particular articles the
person viewed. See Pen Register 

(“[I]f
the user then enters a search phrase [in the Google search engine], that
search phrase would appear in the URL after the first forward slash. This
would reveal content . . . .”).
148                  UNITED STATES v. FORRESTER
operation of a large Ecstasy-manufacturing laboratory, and
were convicted on all counts following a jury trial. They now
appeal their convictions and sentences.

   Forrester moved to represent himself prior to trial. At the
hearing on this motion, the district court carefully warned
Forrester of the dangers of self-representation, but did not
inform him of the charge against him and told him that he
faced 10 years to life in prison whereas he actually faced a
potential prison term of zero to 20 years. The omission and
the misstatement compel us to hold that Forrester’s waiver of
his right to counsel was not knowing and intelligent and that
the Sixth Amendment was violated when he was allowed to
proceed pro se. Accordingly, we reverse Forrester’s convic-
tion and sentence.

   Alba challenges the validity of computer surveillance that
enabled the government to learn the to/from addresses of his
e mail messages, the Internet protocol (“IP”) addresses of the
websites that he visited and the total volume of information
transmitted to or from his account. We conclude that this sur-
veillance was analogous to the use of a pen register that the
Supreme Court held in Smith v. Maryland, 

(1979), did not constitute a search for Fourth Amendment
purposes. Moreover, whether or not the surveillance came
within the scope of the then-applicable federal pen register
statute, Alba is not entitled to the suppression of the evidence
obtained through the surveillance because there is no statutory
or other authority for such a remedy.1
  1
   Alba’s remaining arguments are addressed in a concurrently filed
memorandum disposition. As requested by the parties, we vacate his con-
viction and sentence for conspiracy to manufacture and distribute Ecstasy.
We otherwise affirm Alba’s convictions and sentences, but reduce his
supervised release term from six to five years.
                   UNITED STATES v. FORRESTER                  149
                        I.   BACKGROUND

   Following a lengthy government investigation, Forrester
and Alba were indicted on October 26, 2001, and arraigned
shortly thereafter. Forrester was charged with one count of
conspiracy to manufacture and distribute 3, 4-
methylenedioxymethamphetamine (“Ecstasy”) in violation of
21 U.S.C. §§ 841(a)(1), 846. Alba was also charged with that
offense, as well as with engaging in a continuing criminal
enterprise in violation of 21 U.S.C. § 848(a), conspiracy to
transfer funds outside the United States in promotion of an
illegal activity in violation of 18 U.S.C. § 1956(a)(2)(A)(i),
(h) and conspiracy to conduct financial transactions involving
the proceeds of an illegal activity in violation of 18 U.S.C.
§ 1956(a)(1)(A)(i), (h). Both defendants pleaded not guilty to
all charges.

   Forrester is represented by counsel on appeal. He also had
legal representation from the time his indictment was filed
until October 23, 2002, when the district court heard and
granted his motion to represent himself, as well as during
some of the post-trial proceedings. At the October 23 hearing,
the court repeatedly warned Forrester that defendants who
represent themselves rarely succeed. The court said to For-
rester, for example, “I want to unequivocally tell you and
strongly recommend to you that you don’t do this. In most
cases it’s a disaster,” and “in all cases it is not a good idea for
a nonlawyer to oppose a lawyer in a criminal trial.” Forrester,
in turn, repeatedly assured the court that he understood the
implications of his decision and wished to proceed pro se. He
told the court that he was “aware of the consequences” and
that “I’m coherent and I’m literate and I understand what my
consequences are.” Unfortunately, the court did not apprise
Forrester of the charge against him at the hearing, and gave
him incorrect information about the potential sentence that he
faced. The court said that he faced “a mandatory minimum of
ten years in jail and possibly up to life.” In fact, Forrester
150                 UNITED STATES v. FORRESTER
faced no mandatory minimum and a maximum of 20 years in
prison.2

   The district court held a follow-up hearing on March 7,
2003 to find out how Forrester was coping with self-
representation. The court confirmed that Forrester had access
to discovery materials, instructed him to be more timely with
his motions and rejected his request for the appointment of a
new standby attorney. However, the court again did not
inform Forrester of the charge against him, nor did it correct
its error about his potential sentence. The court’s omission
and misstatement were not corrected at any other point before
trial.

   During its investigation of Forrester and Alba’s Ecstasy-
manufacturing operation, the government employed various
computer surveillance techniques to monitor Alba’s e-mail
and Internet activity. The surveillance began in May 2001
after the government applied for and received court permis-
sion to install a pen register analogue known as a “mirror
port” on Alba’s account with PacBell Internet. The mirror
port was installed at PacBell’s connection facility in San
Diego, and enabled the government to learn the to/from
addresses of Alba’s e-mail messages, the IP addresses of the
websites that Alba visited and the total volume of information
sent to or from his account. Later, the government obtained a
warrant authorizing it to employ imaging and keystroke moni-
toring techniques, but Alba does not challenge on appeal
those techniques’ legality or the government’s application to
use them.

   Forrester and Alba were tried by jury. At trial, the govern-
ment introduced extensive evidence showing that they and
their associates built and operated a major Ecstasy laboratory.
  2
    The maximum was increased to 30 years when, just before trial, the
government filed an information informing the court of Forrester’s prior
felony drug convictions.
                  UNITED STATES v. FORRESTER                151
Witnesses described the lab as “very, very large,” and seized
documents show that it was intended to produce approxi-
mately 440 kilograms of Ecstasy (and $10 million in profit)
per month. The government also presented evidence that Alba
purchased precursor chemicals for Ecstasy, that Forrester met
with a Swedish chemist in Stockholm to learn about manufac-
turing Ecstasy, that the defendants first tried to construct the
lab in two other locations before settling on Escondido, Cali-
fornia and that the Escondido lab was located inside an insu-
lated sea/land container and contained an array of devices and
chemicals used to make Ecstasy.

   The jury convicted Forrester and Alba on all counts. The
district court sentenced them each to 360 months in prison
and six years of supervised release. Both defendants timely
appealed.

                  II.   STANDARD OF REVIEW

  The validity of a waiver of the right to counsel is reviewed
de novo. United States v. Erskine, 

, 1166 (9th
Cir. 2004). Conclusions of law underlying the denial of a
motion to suppress evidence are also reviewed de novo.
United States v. Vesikuru, 

, 1119 (9th Cir.
2002).

                        III.   DISCUSSION

A.   Waiver of the Right to Counsel

   Forrester argues that his waiver of the right to counsel at
the October 23, 2002 hearing was not knowing and intelligent
because the district court failed to inform him of the charge
against him and misinformed him about the potential sentence
he faced. As a result, Forrester contends, his conviction and
sentence must be reversed. We agree with Forrester as to both
the constitutional violation and the requisite remedy.
152               UNITED STATES v. FORRESTER
   [1] Faretta v. California, 

(1975), held that a
defendant has a constitutional right to represent himself but
that “the accused must knowingly and intelligently forgo
those relinquished benefits. . . . [H]e should be made aware
of the dangers and disadvantages of self-representation, so
that the record will establish that he knows what he is doing
and his choice is made with eyes open.” 

(internal
quotations omitted). This court has gleaned a three-factor test
from Faretta, under which “[i]n order to deem a defendant’s
Faretta waiver knowing and intelligent, the district court must
insure that he understands 1) the nature of the charges against
him, 2) the possible penalties, and 3) the ‘dangers and disad-
vantages of self-representation.’ ” 

(quoting United States v. Balough, 

, 1487 (9th
Cir. 1987)). On appeal, the burden of establishing the legality
of the waiver is on the government, 

indulge
in every reasonable presumption against waiver,” United
States v. Arlt, 

, 520-21 (9th Cir. 1994) (quoting
Brewer v. Williams, 

, 404 (1977)). See also
United States v. Mohawk, 

, 1484 (9th Cir. 1994)
(describing the government’s burden as “a heavy one”). Ordi-
narily, only the defendant’s colloquy with the court at the
Faretta hearing is relevant to the waiver analysis. 

a “limited exception” exists whereby “a district court’s
failure to discuss each of the elements in open court will not
necessitate automatic reversal when the record as a whole
reveals a knowing and intelligent waiver.” 

.

   [2] Here the district court clearly apprised Forrester of the
“dangers and disadvantages of self-representation” at the
Faretta hearing. It “unequivocally” and “strongly” recom-
mended against waiving his right to counsel, told him that
“[i]n most cases it’s a disaster” and described in detail the
many unfamiliar tasks he would have to carry out if he took
charge of his own defense. However, the district court failed
to advise Forrester of the “nature of the charge[ ] against
him.” 

. There is no mention of the
                  UNITED STATES v. FORRESTER                153
conspiracy charge in the hearing transcript, let alone any indi-
cation that the court sought to ensure that Forrester under-
stood the charge and grasped that conspiracy is a particularly
complex and confusing allegation to defend against. Further-
more, the district court did not accurately describe the “possi-
ble penalties” faced by Forrester. 

told him that
he faced 10 years to life in prison, whereas he actually faced
the materially different sentence range of zero to 20 years in
prison.

   [3] On this record, the government cannot meet its burden
of showing that Forrester’s waiver of the right to counsel was
knowing and intelligent — especially given our case law that
the government has a heavy burden and that we must indulge
in all reasonable presumptions against waiver. See 

; 

. Of course, Forrester
may have correctly understood the charge against him and the
potential penalties, but the government has failed to prove that
he did so. There is simply no evidence in the Faretta hearing
transcript, which is ordinarily the only part of the record to
which we look, that Forrester was informed of or compre-
hended the charge and penalties. See 

(“We think Mohawk’s decision to waive his right to
counsel may well have been knowing and intelligent — but
we are not free from doubt. . . . We therefore hold that the
government has failed to carry its burden . . . .”); United
States v. Crowhurst, 

, 390 (9th Cir. 1979) (per
curiam) (“[A]n accused individual must specifically be made
aware of the charges and their possible penalties and sanc-
tions.”).

   [4] The government argues that there was no Sixth Amend-
ment violation because the district court overstated the penal-
ties that Forrester faced. According to the government, a
defendant’s right to counsel is not thereby violated because he
would have been more likely to waive that right had he
known the actual, lower penalties he faced. The first flaw in
this argument — which the government fails to support with
154               UNITED STATES v. FORRESTER
any legal authority — is that it is not clear how a defendant’s
decision to waive his right to counsel may be affected by
incorrect information about his potential sentence. It may be,
as in Erskine, that a defendant is more likely to waive his
right to counsel when he is told the stakes are lower than they
actually are. On the other hand, as Forrester contends, it may
be that a middle-aged defendant is more prone to roll the dice
with self-representation when he distrusts his lawyer and is
told that, no matter what he does, he will be in jail for at least
a decade if he is convicted. Had Forrester known that the
stakes were lower and that he faced no mandatory minimum
sentence, he may have been more likely to keep his attorney
despite his misgivings about the attorney’s skill and commit-
ment to his case. Cf. United States v. Stubbs, 

,
411 (6th Cir. 2002) (“When the maximum possible sentence
exposure is overstated, the defendant might well be influ-
enced to accept a plea agreement he would otherwise reject.”)
(internal quotation marks omitted). The causal connection the
government suggests exists between information about one’s
potential sentence and waiver of the right to counsel may be
plausible, but it is far from inevitable.

   [5] The second problem with the government’s sentence
overstatement argument is that it is in essence a harmless
error claim. The government contends, though not in so many
words, that even though Forrester was unaware of the actual
penalty he faced, there was no harm because he would have
waived counsel even if he had been properly informed. But
this court has repeatedly rejected harmless error analysis in
the Faretta waiver context. See 

(“[T]he failure to meet the requirements for a valid Faretta
waiver constitutes per se prejudicial error, and the harmless
error standard is inapplicable.”); 

(invalid Faretta waiver “requires automatic reversal of a
defendant’s conviction”); 

; cf.
McKaskle v. Wiggins, 

, 177 n.8 (1984) (“Since
the right of self-representation is a right that when exercised
usually increases the likelihood of a trial outcome unfavorable
                      UNITED STATES v. FORRESTER                         155
to the defendant, its denial is not amenable to ‘harmless error’
analysis.”). It is thus irrelevant whether the district court over-
stated or understated Forrester’s potential penalty. By materi-
ally misstating the applicable sentence, the court failed to
fulfill its obligation to “insure that [the defendant] under-
stands . . . the possible penalties,” and Forrester’s waiver was
therefore not knowing and intelligent. 

.3

   The government also invokes the “limited exception” that
allows courts to consider the record as a whole rather than
solely the Faretta hearing transcript when determining the
validity of a waiver. See 

. How-
ever, this limited exception is meant to be applied only in
“rare cases.” United States v. Harris, 

, 324 (9th
Cir. 1982); see also United States v. Rylander, 

,
1005 (9th Cir. 1983) (“It is an unusual case where, absent [a
proper] colloquy, a knowing and intelligent waiver of counsel
will be found.”). In addition, Forrester’s active involvement in
his own defense, although probative, is insufficient to show
that his waiver of the right to counsel was knowing and intel-
ligent. See 

(“[T]he mere fact that
a criminal defendant has been repeatedly exposed to the legal
process and has even represented himself before cannot, with-
out more, suffice to support a finding of a knowing and intel-
ligent waiver.”). Finally, the government, both in its briefing
and at oral argument, was unable to point to any evidence in
the record that concretely establishes Forrester’s understand-
  3
    Moreover, even if the Sixth Amendment were not violated when a dis-
trict court materially overstates a defendant’s potential sentence at a
Faretta hearing, there is still the issue of the conspiracy charge against
Forrester, whose nature the district court did not explain to Forrester at the
hearing or anywhere else in the record. See United States v. Dujanovic,

, 186 (9th Cir. 1973) (“We cannot visualize a less minimal
requirement than the District Court shall not grant a request to waive
counsel . . . without . . . determining on the record that the demand to
waive counsel . . . is competently and intelligently made with understand-
ing of the nature of the charge . . . .”).
156                  UNITED STATES v. FORRESTER
ing of the charge against him and potential penalties, nor have
we been able to locate any. Notably, Forrester was not specifi-
cally informed that he was being charged with conspiracy to
manufacture and distribute Ecstasy at any of the three arraign-
ments at which he was present; nor, at the March 7, 2003
follow-up hearing, did the district court correct its error as to
Forrester’s potential sentence or discuss the charge against
him.

   [6] We therefore hold that Forrester’s waiver of the right to
counsel was not knowing and intelligent and that the Sixth
Amendment was violated as a result. Because harmless error
analysis does not apply in this context, we have no choice but
to reverse Forrester’s conviction and sentence. Cf. United
States v. Keen, 

, 429-30 (9th Cir. 1996)
(“Regrettably, given the overwhelming evidence of Keen’s
guilt and the inconvenience a retrial would impose . . . this
discussion appears insufficient. . . . [He] is entitled to a rever-
sal and an opportunity to make an informed and knowing
choice.”).

B.    Computer Surveillance

   Alba contends that the government’s surveillance of his e-
mail and Internet activity violated the Fourth Amendment and
fell outside the scope of the then-applicable federal pen regis-
ter statute.4 We hold that the surveillance did not constitute a
  4
    As mentioned earlier, Alba complains only about the initial surveil-
lance through which the government obtained the to/from addresses of his
e-mail messages, the IP addresses of the websites that he visited and the
total volume of information sent to or from his account. He does not chal-
lenge the more intrusive imaging and keystroke monitoring that subse-
quently took place (though he does argue that the information obtained
through those techniques should be suppressed as tainted derivative evi-
dence).
  Alba did not explicitly move to suppress evidence obtained through the
computer surveillance before the district court. However, both parties have
                      UNITED STATES v. FORRESTER                         157
Fourth Amendment search and thus was not unconstitutional.
We also hold that whether or not the computer surveillance
was covered by the then-applicable pen register statute — an
issue that we do not decide — Alba is not entitled to the sup-
pression of any evidence (let alone the reversal of his convic-
tions) as a consequence.

  1.    The Fourth Amendment

   [7] The Supreme Court held in Smith v. Maryland, 

(1979), that the use of a pen register (a device that
records numbers dialed from a phone line) does not constitute
a search for Fourth Amendment purposes. 

According to the Court, people do not have a subjective
expectation of privacy in numbers that they dial because they
“realize that they must ‘convey’ phone numbers to the tele-
phone company, since it is through telephone company
switching equipment that their calls are completed.” 

Even if there were such a subjective expectation, it
would not be one that society is prepared to recognize as rea-
sonable because “a person has no legitimate expectation of
privacy in information he voluntarily turns over to third par-
ties.” 

Therefore the use of a pen register is not
a Fourth Amendment search. Importantly, the Court distin-
guished pen registers from more intrusive surveillance tech-
niques on the ground that “pen registers do not acquire the
contents of communications” but rather obtain only the
addressing information associated with phone calls. 

see also 

(“Although petitioner’s conduct may have
been calculated to keep the contents of his conversation pri-
vate, his conduct was not and could not have been calculated

briefed the constitutional and statutory issues raised by the surveillance,
and the government does not contend that Alba has waived his Fourth
Amendment and statutory claims. See Tokatly v. Ashcroft, 

,
618 (9th Cir. 2004) (“[I]t is well-established that the government can
‘waive waiver’ implicitly by failing to assert it.”) (internal quotation omit-
ted).
158                  UNITED STATES v. FORRESTER
to preserve the privacy of the number he dialed.”); cf. Katz v.
United States, 

(1967) (legitimate expectation of
privacy exists in contents of phone conversation).

   [8] Neither this nor any other circuit has spoken to the con-
stitutionality of computer surveillance techniques that reveal
the to/from addresses of e-mail messages, the IP addresses of
websites visited and the total amount of data transmitted to or
from an account.5 We conclude that the surveillance tech-
niques the government employed here are constitutionally
indistinguishable from the use of a pen register that the Court
approved in Smith. First, e-mail and Internet users, like the
telephone users in Smith, rely on third-party equipment in
order to engage in communication. Smith based its holding
that telephone users have no expectation of privacy in the
numbers they dial on the users’ imputed knowledge that their
calls are completed through telephone company switching

. Analogously, e-mail and Internet
users have no expectation of privacy in the to/from addresses
of their messages or the IP addresses of the websites they visit
because they should know that this information is provided to
and used by Internet service providers for the specific purpose
of directing the routing of information. Like telephone num-
bers, which provide instructions to the “switching equipment
that processed those numbers,” e-mail to/from addresses and
IP addresses are not merely passively conveyed through third
party equipment, but rather are voluntarily turned over in
order to direct the third party’s servers. 

  5
   Every computer or server connected to the Internet has a unique IP
address. A website typically has only one IP address even though it may
contain hundreds or thousands of pages. For example, Google’s IP address
is 209.85.129.104 and the New York Times’ website’s IP address is
199.239.137.200. See In re Application of the United States of America for
an Order Authorizing the Use of a Pen Register and Trap on [xxx] Inter-
net Service Account/User Name [xxxxxxxx@xxx.com], 

,
48 (D. Mass. 2005) (“Pen Register Application”) (citing government
application that defined “IP address” as a “ ‘unique numerical address
identifying each computer on the [I]nternet’ ”).
                      UNITED STATES v. FORRESTER                        159
   [9] Second, e-mail to/from addresses and IP addresses con-
stitute addressing information and do not necessarily reveal
any more about the underlying contents of communication
than do phone numbers. When the government obtains the to/
from addresses of a person’s e-mails or the IP addresses of
websites visited, it does not find out the contents of the mes-
sages or know the particular pages on the websites the person
viewed. At best, the government may make educated guesses
about what was said in the messages or viewed on the web-
sites based on its knowledge of the e-mail to/from addresses
and IP addresses — but this is no different from speculation
about the contents of a phone conversation on the basis of the
identity of the person or entity that was dialed. Like IP
addresses, certain phone numbers may strongly indicate the
underlying contents of the communication; for example, the
government would know that a person who dialed the phone
number of a chemicals company or a gun shop was likely
seeking information about chemicals or firearms. Further,
when an individual dials a pre-recorded information or
subject-specific line, such as sports scores, lottery results or
phone sex lines, the phone number may even show that the
caller had access to specific content information. Nonetheless,
the Court in Smith and Katz drew a clear line between unpro-
tected addressing information and protected content informa-
tion that the government did not cross here.6
  6
    Surveillance techniques that enable the government to determine not
only the IP addresses that a person accesses but also the uniform resource
locators (“URL”) of the pages visited might be more constitutionally prob-
lematic. A URL, unlike an IP address, identifies the particular document
within a website that a person views and thus reveals much more informa-
tion about the person’s Internet activity. For instance, a surveillance tech-
nique that captures IP addresses would show only that a person visited the
New York Times’ website at http://www.nytimes.com, whereas a tech-
nique that captures URLs would also divulge the particular articles the
person viewed. See Pen Register 

(“[I]f
the user then enters a search phrase [in the Google search engine], that
search phrase would appear in the URL after the first forward slash. This
would reveal content . . . .”).
160               UNITED STATES v. FORRESTER
   [10] The government’s surveillance of e-mail addresses
also may be technologically sophisticated, but it is conceptu-
ally indistinguishable from government surveillance of physi-
cal mail. In a line of cases dating back to the nineteenth
century, the Supreme Court has held that the government can-
not engage in a warrantless search of the contents of sealed
mail, but can observe whatever information people put on the
outside of mail, because that information is voluntarily trans-
mitted to third parties. See United States v. Jacobsen, 

, 114 (1984) (stating that warrantless searches of let-
ters and sealed packages are “presumptively unreasonable”);
United States v. Van Leeuwen, 

, 251-52 (1970)
(mail is “free from inspection . . . except in the manner pro-
vided by the Fourth Amendment,” but postal authorities could
nonetheless detain mail without warrant based on suspicious
appearance and circumstances); Ex parte Jackson, 

, 733 (1877) (“Letters and sealed packages of this kind in
the mail are as fully guarded from examination and inspec-
tion, except as to their outward form and weight, as if they
were retained by the parties forwarding them in their own
domiciles.”); see also United States v. Hernandez, 

, 1209-10 (9th Cir. 2002) (“Although a person has a
legitimate interest that a mailed package will not be opened
and searched en route, there can be no reasonable expectation
that postal service employees will not handle the package or
that they will not view its exterior.”) (internal citation omit-
ted). E-mail, like physical mail, has an outside address “visi-
ble” to the third-party carriers that transmit it to its intended
location, and also a package of content that the sender pre-
sumes will be read only by the intended recipient. The privacy
interests in these two forms of communication are identical.
The contents may deserve Fourth Amendment protection, but
the address and size of the package do not.

  Finally, the pen register in Smith was able to disclose not
only the phone numbers dialed but also the number of calls
made. There is no difference of constitutional magnitude
between this aspect of the pen register and the government’s
                    UNITED STATES v. FORRESTER                      161
monitoring here of the total volume of data transmitted to or
from Alba’s account. Devices that obtain addressing informa-
tion also inevitably reveal the amount of information coming
and going, and do not thereby breach the line between mere
addressing and more content-rich information.

   [11] We therefore hold that the computer surveillance tech-
niques that Alba challenges are not Fourth Amendment
searches. However, our holding extends only to these particu-
lar techniques and does not imply that more intrusive tech-
niques or techniques that reveal more content information are
also constitutionally identical to the use of a pen register.

  2.   The Then-Applicable Pen Register Statute

   Alba claims that the government’s computer surveillance
was not only unconstitutional but also beyond the scope of the
then-applicable pen register statute, 18 U.S.C. § 3121-27
(amended October 2001).7 Under both the old and new ver-
sions of 18 U.S.C. § 3122, the government must apply for and
obtain a court order before it can install and use a pen register.
When the surveillance at issue here took place in May-July
2001, the applicable statute defined a pen register as a “device
which records or decodes electronic or other impulses which
identify the numbers dialed or otherwise transmitted on the
telephone line to which such device is attached.” 18 U.S.C.
§ 3127(3). Notwithstanding the government’s invocation of
this provision and application for and receipt of a court order,
Alba maintains that the computer surveillance at issue here
did not come within the statutory definition of a “pen regis-
ter.”

  [12] Even assuming that Alba is correct in this contention,
he would not be entitled to the suppression of the evidence
obtained through the computer surveillance. As both the
  7
   Unless otherwise noted, all citations are to the pre-October 2001 ver-
sion of the pen register statute.
162               UNITED STATES v. FORRESTER
Supreme Court and this court have emphasized, suppression
is a disfavored remedy, imposed only where its deterrence
benefits outweigh its substantial social costs or (outside the
constitutional context) where it is clearly contemplated by the
relevant statute. See, e.g., Hudson v. Michigan, 

, 2163 (2006) (“Suppression of evidence . . . has always
been our last resort, not our first impulse.”); United States v.
Lombera-Camorlinga, 

, 887 (9th Cir. 2000) (en
banc) (citing “the infrequency with which we have allowed an
exclusionary remedy for a non-constitutional harm”). Alba
does not point to any statutory language requiring suppression
when computer surveillance that is similar but not technically
equivalent to a pen register is carried out. Indeed, he does not
even identify what law or regulation the government may
have violated if its surveillance did not come within the scope
of the then-applicable pen register statute. The suppression of
evidence under these circumstances is plainly inappropriate.

   Our conclusion is bolstered by the fact that suppression still
would not be appropriate even if the computer surveillance
was covered by the pen register statute. Assuming the surveil-
lance violated the statute, there is no mention of suppression
of evidence in the statutory text. Cf. 

(holding
that suppression of evidence was not an appropriate remedy
for a violation of Article 36 of the Vienna Convention when
nothing in the text of the treaty suggested such a remedy).
Instead, the only penalty specified is that “[w]hoever know-
ingly violates subsection (a)” by installing or using a pen reg-
ister without first obtaining a court order “shall be fined under
this title or imprisoned not more than one year, or both.” 18
U.S.C. § 3121(d). Where the legislature has already specified
a remedy for a statutory violation, here fines and imprison-
ment, “we would ‘encroach upon the prerogatives’ of Con-
gress were we to authorize a remedy not provided for by
statute.” United States v. Frazin, 

, 1466 (9th
Cir. 1986) (quoting United States v. Chanen, 

,
1313 (9th Cir. 1977)).
                  UNITED STATES v. FORRESTER                163
   [13] Indeed, two circuits have explicitly held (and we have
implied) that evidence obtained in violation of the pen register
statute need not be suppressed. See United States v. Fregoso,

, 1320 (8th Cir. 1995) (“[T]he statutory scheme
[of the pen register statute] does not mandate exclusion of evi-
dence for violations of the statutory requirements.”); United
States v. Thompson, 

, 1249-50 (11th Cir. 1991)
(“We hold that information obtained from a pen register
placed on a telephone can be used as evidence in a criminal
trial even if the court order authorizing its installation does
not comply with the statutory requirements.”); cf. United
States v. Butz, 

, 1383 (9th Cir. 1993) (refusing
to suppress evidence obtained in violation of state pen register
statute). The statutory text, our general reluctance to require
suppression in the absence of statutory authorization, other
circuits’ holdings and our own indirect precedent all therefore
lead us to conclude that suppression is inappropriate even if
the computer surveillance came within the scope of the then-
applicable pen register statute.

   Finally, even if suppression were a valid remedy, any error
in not excluding evidence was harmless. The evidence
obtained through the computer surveillance was never intro-
duced at trial and was used only as a minor portion of the
government’s application for a court order authorizing imag-
ing and keystroke monitoring. There was more than enough
other evidence in that application to generate probable cause
even if the to/from addresses of Alba’s e-mails, the IP
addresses he accessed and the volume of data transmitted to
or from his account had been suppressed. The discussion of
the computer surveillance spanned only four pages of the 45-
page supporting affidavit for the application, and revealed
only that Alba had sent e-mails to Forrester and accessed cer-
tain chemicals websites. The remainder of the affidavit
included extensive — and more incriminating — evidence
obtained through physical surveillance, conventional pen reg-
isters, wiretaps and cooperating witness statements. Much of
this other evidence predated the start of the computer surveil-
164               UNITED STATES v. FORRESTER
lance, and there is no indication that evidence obtained
through the computer surveillance was used to obtain authori-
zation for any of the other surveillance techniques discussed
in the affidavit. See Nix v. Williams, 

, 443-44
(1984) (warrant based in part on tainted evidence still valid if
there were independent sources that created probable cause).

                      IV.   CONCLUSION

   We reverse Forrester’s conviction and sentence because his
waiver of the right to counsel was not knowing and intelli-
gent. As requested by the parties, and for the reasons set forth
in the concurrently filed memorandum disposition, we vacate
Alba’s conviction and sentence for conspiracy to manufacture
and distribute Ecstasy. We also hold that the techniques the
government used to monitor Alba’s e-mail and Internet activ-
ity did not constitute a search for Fourth Amendment pur-
poses and that, whether or not the monitoring came within the
scope of the then-applicable pen register statute, Alba is not
entitled to the suppression of evidence obtained through the
monitoring. Accordingly, we affirm Alba’s other convictions
and sentences, meaning that his prison term remains 360
months while his supervised release term is reduced from six
to five years.

  Forrester’s conviction and sentence are REVERSED.
Alba’s convictions and sentences are AFFIRMED IN PART
AND REVERSED IN PART.