A new mobile service called Trapster lets motorists warn fellow drivers with a cell phone or PDA about speed traps, red-light cameras and other threats to ticket-free driving, according to The Associated Press. Similarly, as you approach a known threat in the database, that same service would send you an audio alert on your cell phone or other compatible mobile device.

Pete Tenereillo, the developer of Trapster, said in the report that police officials haven't yet complained about the service because it encourages drivers to slow down.

The free service can automatically detect a driver's location using a mobile devices' GPS capability, or triangulate via its Wi-Fi radio, in order to get a location from a database run by Skyhook Wireless, according to the article. The database keeps red-light cameras and potential speed trap zones indefinitely, but deletes specific traps after about an hour since it's assumed that officers would move on. There's also a user rating system to help ensure accuracy. Trapster works on smartphones running BlackBerry OS, Symbian, and Windows Mobile; for more information, check out the company's Web site.