The district court refused to suppress 634 pounds of marijuana found in an automobile stopped by border-patrol officers 660 feet from the Mexican border. We affirm the resulting conviction for violating 21 U.S.C. 841(a)(1).

The officers were alerted by electronic sensors which detect human foot traffic across the border. The automobile was one of two which the officers stopped at about six o'clock on a Sunday morning, when they appeared in the vicinity of freshly detected border traffic. Each of the automobiles was occupied by a solitary male. The two appeared to be traveling in tandem.

The practice of illegal aliens to walk across the border and of smugglers to 'back-pack' contraband over the border in remote desert areas between border checkpoints is well known. See United States v. Patterson, 492 F.2d 995 (9th Cir. 1974). The prompt inspection of the first automobile to appear on the highway after the officers received the sensor alarm was not only well-advised, but was based upon a founded suspicion. The officers knew that some person or persons had recently crossed the border illegally and that the two automobiles which were stopped were the only ones known to have been in the sensor-surveillance area near the time of the sensor alert.

The use of the electronic sensor devices is relatively new along the international border. The border patrol does not have enough officers to maintain constant line watch at all times and along all the remote crossing areas. The electronic devices were developed for the military detection of night patrols and infiltrators. The devices are engineered to ignore small animals, but to record an alarm when metal or an animal weighing more than 40 pounds passes nearby. These alarms are recorded in a central station and forwarded by radio to vehicular patrols supplementing the line watch. The trial court was able to find from the government's explanation of the sensor technique adequate foundation for a decision to stop the automobiles in this case. After the automobiles were stopped, the first driver revealed that he was an illegal alien. He was arrested. The ensuing search incidental to the arrest produced the evidence. There was no error.

Affirmed.