esocid writes "In a modern equivalent of flashing your headlights to warn other motorists of police speed traps, you can now warn fellow drivers with a cell phone or personal digital assistant about speed traps, red-light cameras, and other threats to ticket-free driving. And as you approach a known threat, you'll get an audio alert on your mobile device. The developer of Trapster, Pete Tenereillo, said the system, which requires punching in a few keys such as '#1' to submit information to Trapster's database, should comply with laws banning talking on cell phones. The free service can automatically detect location using mobile devices' GPS capabilities or tap their Wi-Fi and get location from a database run by Skyhook Wireless. Police officials that Tenereillo has talked to haven't complained about the service because it inevitably encourages drivers to slow down."