This is the work of American Border Patrol, an emergent and entirely unofficial wing of the country's homeland defense. Last summer, Spencer moved with his wife out from Los Angeles to Sierra Vista, Ariz., to start A.B.P., what he calls a neighborhood watch of the Arizona border. Since this ranch is not a neighborhood but forsaken desert, A.B.P. is more accurately a roving bureau of traffic reporters, dedicated to documenting illegal immigration where it happens. With satellite dishes, ground sensors and dozens of ''hawkeye'' spotters to call in sightings, A.B.P. tracks S.B.I., films them and notifies the Border Patrol while they upload the film live to the Internet. In quasi-military operations like this one, Spencer estimates that A.B.P. has helped capture more than 3,300 illegal immigrants. ''Our policy is not to touch them,'' Spencer says. ''That's the Border Patrol's job. We just want to show people what is happening down here.''

These are people who took the president at his word when he called for every American to stand vigilant and report suspicious activity after 9/11, and who live at one of the few remaining trapdoors into America.

Spencer, having lived in Los Angeles for more than 60 years, has a visceral reaction to illegal immigration....A.B.P. and the other border-control groups have been called vigilantes and militias, but Spencer doesn't carry a gun. He prefers cameras, which may be a more effective weapon when it comes to his cause.

The A.B.P. Web site even allows you to set up an alert so that anytime Spencer finds an S.B.I. on film, you know. ''I want people, when they get up in the morning, to turn on their television and get their border report with their weather report,'' Spencer says. ''Like, 'Ladies and gentlemen, 3,000 people made it across the border last night, and here are videos of them crossing.' ''