VG2 is what police use to sense radar detectors in other cars. In states where radar detection is illegal, VG2 is used to catch people using them. It's often called a "radar detector detector" detectors with VG2 sensing usually use a circuit that shuts off the detector, or puts it into a low power mode to evade the VG2 guns. the polie VG2 works by detecting the oscillating frequency bleed from a radar detector in the PLL circuit used to detect radar frequencies.
Laser detection is debated as to if it really does any good. Laser speed detection works by bouncing a narrow beam of light off of a moving target such as your car, to read the speed. detectors with laser supposedly detect "laser scatter" or light beam reflections bouncing off cars ahead of you. the chance of early detection is actually very improbable, and at best, you get less warning time than it takes to react and slow the car.