In the TomTom satnav system with maps for the UK, you can 'jailbreak' the software and install all the speed cameras in the country onto your satnav. You drive around and get a pinging noise when one is coming up. It's extremely reliable and absolutely brilliant. You can even set it to tell you how many metres away it is, how fast over the limit you are going. Amazing.

Or those dukes of hazzard style 'radar detectors' that sit in the front of the cars and beep when there's a 'cop with a hairdryer' in the area..