Speed traps are meant to snare the unsuspecting speeder.

You know the drill -- you don't notice the police squad car sitting under an overpass or parked in a grassy median until you speed by, uttering a gasp of panic (or something similar) in the process.

Trapster.com gives motorists a heads-up before they end up with their head down while pulled over by a ticket-writing officer.

"In realtime, it tells you where the police are," said creator Pete Tenereillo.

The site, which depends on information shared by users, tells you where the traps are by alerting you via cell phone.

When you see a police officer with a radar detector or other kinds of traps ... or a place where police often hide, you press a button on your phone," Tenereillo said.

There are three ways to use the service: by downloading the Trapster Mobile program to your cell phone, using a toll-free number to report traps or getting SMS or e-mail alerts.

The credibility of each user is rated depending on alert accuracy. A site map shows where traps are located using indicators of different colors.

"The green is a low-confidence trap, the yellow is medium-confidence, and the red is a high-confidence trap," Tenereillo said.

As users approach a speed-trap area, their phone will alert them, saying, "live police," Tenereillo said.

Tenereillo said the site is not meant to help motorists get away with speeding, but to discourage it.

And police agree, saying most drivers will slow down when they know they are approaching a speed trap.