When a laser jammer detects a police officer’s gun, it fires back a return signal that confuses the gun and temporarily prevents it from being able to get a speed reading. This gives you enough time to slow down and disable your laser jammer so the officer can get a reading off your vehicle.
Early laser jammers used simple brute force techniques that blasted a bunch of fake laser signals back.
Newer laser jammers are much more intentional about when the send back jamming pulses.