(Slip Opinion)              OCTOBER TERM, 2012                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 

, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

                           FLORIDA v. HARRIS

        CERTIORARI TO THE SUPREME COURT OF FLORIDA

  No. 11–817.      Argued October 31, 2012—Decided February 19, 2013
Officer Wheetley pulled over respondent Harris for a routine traffic
  stop. Observing Harris’s nervousness and an open beer can, Wheet-
  ley sought consent to search Harris’s truck. When Harris refused,
  Wheetley executed a sniff test with his trained narcotics dog, Aldo.
  The dog alerted at the driver’s-side door handle, leading Wheetley to
  conclude that he had probable cause for a search. That search turned
  up nothing Aldo was trained to detect, but did reveal pseudoephed-
  rine and other ingredients for manufacturing methamphetamine.
  Harris was arrested and charged with illegal possession of those in-
  gredients. In a subsequent stop while Harris was out on bail, Aldo
  again alerted on Harris’s truck but nothing of interest was found. At
  a suppression hearing, Wheetley testified about his and Aldo’s exten-
  sive training in drug detection. Harris’s attorney did not contest the
  quality of that training, focusing instead on Aldo’s certification and
  performance in the field, particularly in the two stops of Harris’s
  truck. The trial court denied the motion to suppress, but the Florida
  Supreme Court reversed. It held that a wide array of evidence was
  always necessary to establish probable cause, including field-
  performance records showing how many times the dog has falsely
  alerted. If an officer like Wheetley failed to keep such records, he
  could never have probable cause to think the dog a reliable indicator
  of drugs.
Held: Because training and testing records supported Aldo’s reliability
 in detecting drugs and Harris failed to undermine that evidence,
 Wheetley had probable cause to search Harris’s truck. Pp. 5–11.
    (a) In testing whether an officer has probable cause to conduct a
 search, all that is required is the kind of “fair probability” on which
 “reasonable and prudent [people] act.” Illinois v. Gates, 

, 235. To evaluate whether the State has met this practical and
2                          FLORIDA v. HARRIS

                                  Syllabus

    common-sensical standard, this Court has consistently looked to the
    totality of the circumstances and rejected rigid rules, bright-line
    tests, and mechanistic inquiries. Ibid.
       The Florida Supreme Court flouted this established approach by
    creating a strict evidentiary checklist to assess a drug-detection dog’s
    reliability. Requiring the State to introduce comprehensive docu-
    mentation of the dog’s prior hits and misses in the field, and holding
    that absent field records will preclude a finding of probable cause no
    matter how much other proof the State offers, is the antithesis of a
    totality-of-the-circumstances approach. This is made worse by the
    State Supreme Court’s treatment of field-performance records as the
    evidentiary gold standard when, in fact, such data may not capture a
    dog’s false negatives or may markedly overstate a dog’s false posi-
    tives. Such inaccuracies do not taint records of a dog’s performance
    in standard training and certification settings, making that perfor-
    mance a better measure of a dog’s reliability. Field records may
    sometimes be relevant, but the court should evaluate all the evi-
    dence, and should not prescribe an inflexible set of requirements.
       Under the correct approach, a probable-cause hearing focusing on a
    dog’s alert should proceed much like any other, with the court allow-
    ing the parties to make their best case and evaluating the totality of
    the circumstances. If the State has produced proof from controlled
    settings that a dog performs reliably in detecting drugs, and the de-
    fendant has not contested that showing, the court should find proba-
    ble cause. But a defendant must have an opportunity to challenge
    such evidence of a dog’s reliability, whether by cross-examining the
    testifying officer or by introducing his own fact or expert witnesses.
    The defendant may contest training or testing standards as flawed or
    too lax, or raise an issue regarding the particular alert. The court
    should then consider all the evidence and apply the usual test for
    probable cause—whether all the facts surrounding the alert, viewed
    through the lens of common sense, would make a reasonably prudent
    person think that a search would reveal contraband or evidence of a
    crime. Pp. 5–9.
       (b) The record in this case amply supported the trial court’s deter-
    mination that Aldo’s alert gave Wheetley probable cause to search
    the truck. The State introduced substantial evidence of Aldo’s train-
    ing and his proficiency in finding drugs. Harris declined to challenge
    any aspect of that training or testing in the trial court, and the Court
    does not consider such arguments when they are presented for this
    first time in this Court. Harris principally relied below on Wheetley’s
    failure to find any substance that Aldo was trained to detect. That
    infers too much from the failure of a particular alert to lead to drugs,
    and did not rebut the State’s evidence from recent training and test-
                     Cite as: 568 U. S. ____ (2013)         3

                               Syllabus

  ing. Pp. 9–11.

, reversed.

  KAGAN, J., delivered the opinion for a unanimous Court.
                        Cite as: 568 U. S. ____ (2013)                              1

                             Opinion of the Court

     NOTICE: This opinion is subject to formal revision before publication in the
     preliminary print of the United States Reports. Readers are requested to
     notify the Reporter of Decisions, Supreme Court of the United States, Wash-
     ington, D. C. 20543, of any typographical or other formal errors, in order
     that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                   _________________

                                   No. 11–817
                                   _________________


     FLORIDA, PETITIONER v. CLAYTON HARRIS
    ON WRIT OF CERTIORARI TO THE SUPREME COURT OF

                       FLORIDA

                              [February 19, 2013]


   JUSTICE KAGAN delivered the opinion of the Court.
   In this case, we consider how a court should determine
if the “alert” of a drug-detection dog during a traffic stop
provides probable cause to search a vehicle. The Florida
Supreme Court held that the State must in every case
present an exhaustive set of records, including a log of the
dog’s performance in the field, to establish the dog’s relia-
bility. See 

, 775 (2011). We think that de-
mand inconsistent with the “flexible, common-sense
standard” of probable cause. Illinois v. Gates, 

, 239 (1983).
                             I
   William Wheetley is a K–9 Officer in the Liberty County,
Florida Sheriff ’s Office. On June 24, 2006, he was on a
routine patrol with Aldo, a German shepherd trained to
detect certain narcotics (methamphetamine, marijuana,
cocaine, heroin, and ecstasy). Wheetley pulled over re-
spondent Clayton Harris’s truck because it had an expired
license plate. On approaching the driver’s-side door,
Wheetley saw that Harris was “visibly nervous,” unable to
sit still, shaking, and breathing rapidly. Wheetley also
noticed an open can of beer in the truck’s cup holder. App.
2                    FLORIDA v. HARRIS

                      Opinion of the Court

62. Wheetley asked Harris for consent to search the truck,
but Harris refused. At that point, Wheetley retrieved Aldo
from the patrol car and walked him around Harris’s truck
for a “free air sniff.” Id., at 63. Aldo alerted at the
driver’s-side door handle—signaling, through a distinctive
set of behaviors, that he smelled drugs there.
  Wheetley concluded, based principally on Aldo’s alert,
that he had probable cause to search the truck. His search
did not turn up any of the drugs Aldo was trained to de-
tect. But it did reveal 200 loose pseudoephedrine pills,
8,000 matches, a bottle of hydrochloric acid, two contain-
ers of antifreeze, and a coffee filter full of iodine crystals—
all ingredients for making methamphetamine. Wheetley
accordingly arrested Harris, who admitted after proper
Miranda warnings that he routinely “cooked” metham-
phetamine at his house and could not go “more than a few
days without using” it. Id., at 68. The State charged
Harris with possessing pseudoephedrine for use in manu-
facturing methamphetamine.
  While out on bail, Harris had another run-in with
Wheetley and Aldo. This time, Wheetley pulled Harris
over for a broken brake light. Aldo again sniffed the
truck’s exterior, and again alerted at the driver’s-side door
handle. Wheetley once more searched the truck, but on
this occasion discovered nothing of interest.
  Harris moved to suppress the evidence found in his
truck on the ground that Aldo’s alert had not given Wheet-
ley probable cause for a search. At the hearing on that
motion, Wheetley testified about both his and Aldo’s train-
ing in drug detection. See id., at 52–82. In 2004, Wheet-
ley (and a different dog) completed a 160-hour course in
narcotics detection offered by the Dothan, Alabama Police
Department, while Aldo (and a different handler) completed
a similar, 120-hour course given by the Apopka, Florida
Police Department. That same year, Aldo received a one-
year certification from Drug Beat, a private company that
                 Cite as: 568 U. S. ____ (2013)           3

                     Opinion of the Court

specializes in testing and certifying K–9 dogs. Wheetley
and Aldo teamed up in 2005 and went through another,
40-hour refresher course in Dothan together. They also
did four hours of training exercises each week to maintain
their skills. Wheetley would hide drugs in certain ve-
hicles or buildings while leaving others “blank” to deter-
mine whether Aldo alerted at the right places. Id., at 57.
According to Wheetley, Aldo’s performance in those exer-
cises was “really good.” Id., at 60. The State introduced
“Monthly Canine Detection Training Logs” consistent with
that testimony: They showed that Aldo always found
hidden drugs and that he performed “satisfactorily” (the
higher of two possible assessments) on each day of train-
ing. Id., at 109–116.
   On cross-examination, Harris’s attorney chose not to
contest the quality of Aldo’s or Wheetley’s training. She
focused instead on Aldo’s certification and his performance
in the field, particularly the two stops of Harris’s truck.
Wheetley conceded that the certification (which, he noted,
Florida law did not require) had expired the year before
he pulled Harris over. See id., at 70–71. Wheetley also
acknowledged that he did not keep complete records of
Aldo’s performance in traffic stops or other field work;
instead, he maintained records only of alerts resulting in
arrests. See id., at 71–72, 74. But Wheetley defended
Aldo’s two alerts to Harris’s seemingly narcotics-free
truck: According to Wheetley, Harris probably transferred
the odor of methamphetamine to the door handle, and
Aldo responded to that “residual odor.” Id., at 80.
   The trial court concluded that Wheetley had probable
cause to search Harris’s truck and so denied the motion to
suppress. Harris then entered a no-contest plea while
reserving the right to appeal the trial court’s ruling. An
intermediate state court summarily affirmed. See 

, 1215 (2008) (per curiam).
   The Florida Supreme Court reversed, holding that
4                   FLORIDA v. HARRIS

                     Opinion of the Court

Wheetley lacked probable cause to search Harris’s vehicle
under the Fourth Amendment. “[W]hen a dog alerts,” the
court wrote, “the fact that the dog has been trained and
certified is simply not enough to establish probable cause.”

, at 767. To demonstrate a dog’s reliability, the
State needed to produce a wider array of evidence:
    “[T]he State must present . . . the dog’s training and
    certification records, an explanation of the meaning of
    the particular training and certification, field perfor-
    mance records (including any unverified alerts), and
    evidence concerning the experience and training of the
    officer handling the dog, as well as any other objective
    evidence known to the officer about the dog’s reliabil-
    ity.” Id., at 775.
The court particularly stressed the need for “evidence of
the dog’s performance history,” including records showing
“how often the dog has alerted in the field without illegal
contraband having been found.” Id., at 769. That data,
the court stated, could help to expose such problems as a
handler’s tendency (conscious or not) to “cue [a] dog to
alert” and “a dog’s inability to distinguish between resid-
ual odors and actual drugs.” Id., at 769, 774. Accordingly,
an officer like Wheetley who did not keep full records of
his dog’s field performance could never have the requisite
cause to think “that the dog is a reliable indicator of
drugs.” Id., at 773.
   Judge Canady dissented, maintaining that the major-
ity’s “elaborate and inflexible evidentiary requirements”
went beyond the demands of probable cause. Id., at 775.
He would have affirmed the trial court’s ruling on the
strength of Aldo’s training history and Harris’s “fail[ure]
to present any evidence challenging” it. Id., at 776.
   We granted certiorari, 566 U. S. ___ (2012), and now
reverse.
                 Cite as: 568 U. S. ____ (2013)            5

                     Opinion of the Court

                               II
   A police officer has probable cause to conduct a search
when “the facts available to [him] would ‘warrant a [per-
son] of reasonable caution in the belief ’” that contraband
or evidence of a crime is present. Texas v. Brown, 

, 742 (1983) (plurality opinion) (quoting Carroll v.
United States, 

, 162 (1925)); see Safford
Unified School Dist. #1 v. Redding, 

, 370–
371 (2009). The test for probable cause is not reducible to
“precise definition or quantification.” Maryland v. Pringle,

, 371 (2003). “Finely tuned standards such
as proof beyond a reasonable doubt or by a preponderance
of the evidence . . . have no place in the [probable-cause]
decision.” Gates, 462 U. S., at 235. All we have required
is the kind of “fair probability” on which “reasonable and
prudent [people,] not legal technicians, act.” Id., at 238,
231 (internal quotation marks omitted).
   In evaluating whether the State has met this practical
and common-sensical standard, we have consistently
looked to the totality of the circumstances. See, e.g., Prin-
gle, 540 U. S., at 371; Gates, 462 U. S., at 232; Brinegar v.
United States, 

, 176 (1949). We have rejected
rigid rules, bright-line tests, and mechanistic inquiries in
favor of a more flexible, all-things-considered approach. In
Gates, for example, we abandoned our old test for as-
sessing the reliability of informants’ tips because it had
devolved into a “complex superstructure of evidentiary
and analytical rules,” any one of which, if not complied
with, would derail a finding of probable cause. 462 U. S.,
at 235. We lamented the development of a list of “inflexi-
ble, independent requirements applicable in every case.”
Id., at 230, n. 6. Probable cause, we emphasized, is “a
fluid concept—turning on the assessment of probabilities
in particular factual contexts—not readily, or even use-
fully, reduced to a neat set of legal rules.” Id., at 232.
   The Florida Supreme Court flouted this established
6                         FLORIDA v. HARRIS

                          Opinion of the Court

approach to determining probable cause. To assess the
reliability of a drug-detection dog, the court created a
strict evidentiary checklist, whose every item the State
must tick off.1 Most prominently, an alert cannot estab-
lish probable cause under the Florida court’s decision
unless the State introduces comprehensive documentation
of the dog’s prior “hits” and “misses” in the field. (One
wonders how the court would apply its test to a rookie
dog.) No matter how much other proof the State offers of
the dog’s reliability, the absent field performance records
will preclude a finding of probable cause. That is the
antithesis of a totality-of-the-circumstances analysis. It
is, indeed, the very thing we criticized in Gates when we
overhauled our method for assessing the trustworthiness
of an informant’s tip. A gap as to any one matter, we
explained, should not sink the State’s case; rather, that
“deficiency . . . may be compensated for, in determining
the overall reliability of a tip, by a strong showing as to . . .
other indicia of reliability.” Id., at 233. So too here, a
finding of a drug-detection dog’s reliability cannot depend
on the State’s satisfaction of multiple, independent eviden-
tiary requirements. No more for dogs than for human
informants is such an inflexible checklist the way to prove
reliability, and thus establish probable cause.
   Making matters worse, the decision below treats records
of a dog’s field performance as the gold standard in evi-
——————
    1 Bythe time of oral argument in this case, even Harris declined to
defend the idea that the Fourth Amendment compels the State to
produce each item of evidence the Florida Supreme Court enumerated.
See Tr. of Oral Arg. 29–30 (“I don’t believe the Constitution requires
[that list]”). Harris instead argued that the court’s decision, although
“look[ing] rather didactic,” in fact did not impose any such requirement.
Id., at 29; see id., at 31 (“[I]t’s not a specific recipe that can’t be de-
viated from”). But in reading the decision below as establishing a man-
datory checklist, we do no more than take the court at its (oft-repeated)
word. See, e.g., 

, 758, 759, 771, 775 (Fla. 2011) (holding
that the State “must” present the itemized evidence).
                      Cite as: 568 U. S. ____ (2013)                      7

                           Opinion of the Court

dence, when in most cases they have relatively limited
import. Errors may abound in such records. If a dog
on patrol fails to alert to a car containing drugs, the mis-
take usually will go undetected because the officer will not
initiate a search. Field data thus may not capture a dog’s
false negatives. Conversely (and more relevant here), if
the dog alerts to a car in which the officer finds no narcot-
ics, the dog may not have made a mistake at all. The dog
may have detected substances that were too well hidden or
present in quantities too small for the officer to locate. Or
the dog may have smelled the residual odor of drugs pre-
viously in the vehicle or on the driver’s person.2 Field data
thus may markedly overstate a dog’s real false positives.
By contrast, those inaccuracies—in either direction—do
not taint records of a dog’s performance in standard train-
ing and certification settings. There, the designers of an
assessment know where drugs are hidden and where they
are not—and so where a dog should alert and where he
——————
  2 See  U. S. Dept. of Army, Military Working Dog Program 30 (Pam-
phlet 190–12, 1993) (“The odor of a substance may be present in enough
concentration to cause the dog to respond even after the substance has
been removed. Therefore, when a detector dog responds and no drug
or explosive is found, do not assume the dog has made an error”);
S. Bryson, Police Dog Tactics 257 (2d ed. 2000) (“Four skiers toke up in
the parking lot before going up the mountain. Five minutes later a
narcotic detector dog alerts to the car. There is no dope inside. How-
ever, the dog has performed correctly”). The Florida Supreme Court
treated a dog’s response to residual odor as an error, referring to the
“inability to distinguish between [such] odors and actual drugs” as a
“facto[r] that call[s] into question Aldo’s reliability.” 

, at 773–
774; see supra, at 4. But that statement reflects a misunderstanding.
A detection dog recognizes an odor, not a drug, and should alert when-
ever the scent is present, even if the substance is gone (just as a police
officer’s much inferior nose detects the odor of marijuana for some time
after a joint has been smoked). In the usual case, the mere chance that
the substance might no longer be at the location does not matter; a
well-trained dog’s alert establishes a fair probability—all that is re-
quired for probable cause—that either drugs or evidence of a drug
crime (like the precursor chemicals in Harris’s truck) will be found.
8                        FLORIDA v. HARRIS

                          Opinion of the Court

should not. The better measure of a dog’s reliability
thus comes away from the field, in controlled testing
environments.3
  For that reason, evidence of a dog’s satisfactory perfor-
mance in a certification or training program can itself
provide sufficient reason to trust his alert. If a bona fide
organization has certified a dog after testing his reliability
in a controlled setting, a court can presume (subject to any
conflicting evidence offered) that the dog’s alert provides
probable cause to search. The same is true, even in the
absence of formal certification, if the dog has recently and
successfully completed a training program that evaluated
his proficiency in locating drugs. After all, law enforce-
ment units have their own strong incentive to use effective
training and certification programs, because only accurate
drug-detection dogs enable officers to locate contraband
without incurring unnecessary risks or wasting limited
time and resources.
  A defendant, however, must have an opportunity to
challenge such evidence of a dog’s reliability, whether by
cross-examining the testifying officer or by introducing his
own fact or expert witnesses. The defendant, for example,
may contest the adequacy of a certification or training
program, perhaps asserting that its standards are too lax
or its methods faulty. So too, the defendant may examine
how the dog (or handler) performed in the assessments
made in those settings. Indeed, evidence of the dog’s (or
handler’s) history in the field, although susceptible to the
kind of misinterpretation we have discussed, may some-
times be relevant, as the Solicitor General acknowledged
——————
   3 See K. Furton, J. Greb, & H. Holness, Florida Int’l Univ., The Scien-

tific Working Group on Dog and Orthogonal Detector Guidelines 1, 61–
62, 66 (2010) (recommending as a “best practice” that a dog’s reliability
should be assessed based on “the results of certification and proficiency
assessments,” because in those “procedure[s] you should know whether
you have a false positive,” unlike in “most operational situations”).
                 Cite as: 568 U. S. ____ (2013)           9

                     Opinion of the Court

at oral argument. See Tr. of Oral Arg. 23–24 (“[T]he
defendant can ask the handler, if the handler is on the
stand, about field performance, and then the court can
give that answer whatever weight is appropriate”). And
even assuming a dog is generally reliable, circumstances
surrounding a particular alert may undermine the case
for probable cause—if, say, the officer cued the dog (con-
sciously or not), or if the team was working under un-
familiar conditions.
   In short, a probable-cause hearing focusing on a dog’s
alert should proceed much like any other. The court
should allow the parties to make their best case, con-
sistent with the usual rules of criminal procedure. And
the court should then evaluate the proffered evidence to
decide what all the circumstances demonstrate. If the
State has produced proof from controlled settings that a
dog performs reliably in detecting drugs, and the defend-
ant has not contested that showing, then the court should
find probable cause. If, in contrast, the defendant has
challenged the State’s case (by disputing the reliability of
the dog overall or of a particular alert), then the court
should weigh the competing evidence. In all events, the
court should not prescribe, as the Florida Supreme Court
did, an inflexible set of evidentiary requirements. The
question—similar to every inquiry into probable cause—is
whether all the facts surrounding a dog’s alert, viewed
through the lens of common sense, would make a reason-
ably prudent person think that a search would reveal con-
traband or evidence of a crime. A sniff is up to snuff when
it meets that test.
                             III
  And here, Aldo’s did. The record in this case amply
supported the trial court’s determination that Aldo’s alert
gave Wheetley probable cause to search Harris’s truck.
  The State, as earlier described, introduced substantial
10                  FLORIDA v. HARRIS

                     Opinion of the Court

evidence of Aldo’s training and his proficiency in finding
drugs. See supra, at 2–3. The State showed that two
years before alerting to Harris’s truck, Aldo had success-
fully completed a 120-hour program in narcotics detection,
and separately obtained a certification from an independ-
ent company. And although the certification expired after
a year, the Sheriff ’s Office required continuing training
for Aldo and Wheetley. The two satisfied the require-
ments of another, 40-hour training program one year prior
to the search at issue. And Wheetley worked with Aldo
for four hours each week on exercises designed to keep
their skills sharp. Wheetley testified, and written records
confirmed, that in those settings Aldo always performed at
the highest level.
   Harris, as also noted above, declined to challenge in the
trial court any aspect of Aldo’s training. See supra, at 3.
To be sure, Harris’s briefs in this Court raise questions
about that training’s adequacy—for example, whether the
programs simulated sufficiently diverse environments and
whether they used enough blind testing (in which the
handler does not know the location of drugs and so cannot
cue the dog). See Brief for Respondent 57–58. Similarly,
Harris here queries just how well Aldo performed in con-
trolled testing. See id., at 58. But Harris never voiced
those doubts in the trial court, and cannot do so for the
first time here. See, e.g., Rugendorf v. United States, 

, 534 (1964). As the case came to the trial court,
Aldo had successfully completed two recent drug-detection
courses and maintained his proficiency through weekly
training exercises. Viewed alone, that training record—
with or without the prior certification—sufficed to estab-
lish Aldo’s reliability. See supra, at 8–9.
   And Harris’s cross-examination of Wheetley, which
focused on Aldo’s field performance, failed to rebut the
State’s case. Harris principally contended in the trial
court that because Wheetley did not find any of the sub-
                 Cite as: 568 U. S. ____ (2013)                 11

                     Opinion of the Court

stances Aldo was trained to detect, Aldo’s two alerts must
have been false. See Brief for Respondent 1; App. 77–80.
But we have already described the hazards of inferring too
much from the failure of a dog’s alert to lead to drugs, see
supra, at 7; and here we doubt that Harris’s logic does
justice to Aldo’s skills. Harris cooked and used metham-
phetamine on a regular basis; so as Wheetley later sur-
mised, Aldo likely responded to odors that Harris had
transferred to the driver’s-side door handle of his truck.
See supra, at 3. A well-trained drug-detection dog should
alert to such odors; his response to them might appear
a mistake, but in fact is not. See n. 2, supra. And still
more fundamentally, we do not evaluate probable cause in
hindsight, based on what a search does or does not turn
up. See United States v. Di Re, 

, 595 (1948).
For the reasons already stated, Wheetley had good cause
to view Aldo as a reliable detector of drugs. And no special
circumstance here gave Wheetley reason to discount Aldo’s
usual dependability or distrust his response to Harris’s
truck.
   Because training records established Aldo’s reliability in
detecting drugs and Harris failed to undermine that show-
ing, we agree with the trial court that Wheetley had prob-
able cause to search Harris’s truck. We accordingly
reverse the judgment of the Florida Supreme Court.

                                                  It is so ordered.