Roadpilot

Great to look at and well built, this boasted the largest screen here. It shows speed, compass heading, time and an arrow pointing in the direction and distance to the nearest trap.

The device warns of a site coming up by using a countdown beep or voice warning, depending on your preference. It worked well, with no GPS loss and no false alarms.

The drawback was the price, plus the fact it's not easy to swap from car to car.