Speed trap is a device used by the officers to measure the speed of your vehicle in a particular area where speed limit is enforced. Radar or laser is used to measure the speed while speed trap is a stationary thing in itself.
The element of stealth is used in the working of a speed trap and can surprise the driver running their vehicle more than the speed limit. The policeman using speed trap mostly remains hidden from the sight so that they cannot be located and can easily trap the speed. Mostly these devices are used in the blind corners, near a turn or under an underpass. In such regions officers have the laser gun which is a radar to trace the speed of moving vehicles that pass from there.
Another type of speed trap is placed on the highway passes or off ramps. Generally a driver drives by looking straight in front and he cannot recognize a laser gun or radar in the hands of an officer pointed towards their vehicle and tracing its speed. To know that a vehicle has passed through a speed trap is a flashing light is seen in the mirror of rear view.
Radar speed traps are used by one officer at a time. One traces the speed of vehicle and informs the other about it. Then driver can be investigated ahead.
Stationary speed traps are also used and are also called as photo radar camera. They are placed near the road or inside another vehicle of the officers, parked near the road. This speed trap not only measures the speed but also take the photographs of driver and license plate as the vehicle passes through the area of speed trap. This helps to find the owner through the photographs of license plate. Now the speeding ticket can be posted to the particular person.