ROSEVILLE, Calif.  Gary Garcia probably knows the early-morning rhythms of the streets here in this city just north of Sacramento better than anyone besides his fellow garbage truck drivers. Anything that breaks the morning pattern is obvious to them, which makes it easy for the garbage collectors to perform an added job  eyes for the police.

“See, here’s an odd vehicle here,” Mr. Garcia said, gesturing toward a red Ford sedan parked by itself, far from the nearest house, on a street where every other vehicle sat neatly in a driveway. He drove by slowly, peering down into the car but seeing nothing on the seats. “It’s an odd place to be parked.”

It is a low-tech approach to surveillance, relying not on satellite cameras, space-age radiation detection devices or even neighborhood Webcams. In more and more towns, drivers and garbage collectors are helping the police keep up with what is happening on the streets.

Some of the nation’s biggest waste collection companies, including Waste Management and Republic Services, have been participating in the program for several years, allowing police departments to train their workers on what to look for.