A laser jammer is a device typically used by motorists in an attempt to counteract the use of light detection and ranging (LIDAR) guns often used by law enforcement to track vehicle speeds. These devices essentially work by sending out a signal that scrambles the returning signal for a LIDAR gun, thereby making the gun unable to properly determine vehicle speed. A laser jammer is not necessarily illegal for use by motorists in all areas, though some countries and regions have outlawed their use.

Also called laser scramblers, a laser jammer sends out a signal that disrupts the use of a LIDAR gun. LIDAR guns are used by many law enforcement departments and allow police officers to quickly and easily determine the speed at which a vehicle is traveling. These guns function in a way similar to radar, hence the name, and send out a pulse of light that is scattered back by a vehicle. The firmware in the gun uses the time it took for the signal to bounce back to determine the speed at which the vehicle is traveling.

A laser jammer sends out a light signal that effectively confuses the firmware in the gun, which makes it unable to properly calculate and display speed. This can be done in a number of different ways, though the most effective method involves a laser jammer that detects incoming signals from a LIDAR gun. Once the signal is detected, then the laser jammer sends out the proper signal to disrupt the effectiveness of the gun, while notifying the driver of the vehicle that he or she is being targeted by a LIDAR gun. The sensor for this type of jammer is often mounted on the front of a vehicle, though some devices can also be mounted on the back or both front and back.

The use of a laser jammer is not necessarily illegal in all areas, though some regions have passed laws to ban the use of such devices. While many countries have laws that forbid the use of radar jammers to disrupt the use of older radar speed detection guns, these laws do not necessarily cover the use of laser jamming devices. In the US, individual states have begun passing laws to ban the use of a laser jammer. This means anyone driving from state to state and using such a jammer should be aware of the legality of using such a device in each state.