When you see a speed trap, red light camera etc, report it by pressing a button on your phone. Other user's phones will alert them as they approach the trap. Trapster® learns the credibility of traps based on how many users agree. It also learns the credibility of each user, over time.
Works great on my iphone and the more users who use it, the better the info that comes through is. Seems to be a fair few in perth already onto it.
Its free too in the apps store. Works on other phones with gps too.
http://www.trapster.com