Its only gonna detect when the radar gun is on. Even if the radar gun isnt pointed at you you will still get comfirmation because of the scattering signal off of streetsigns/other cars. You will notice that cops will even keep the radar gun off until they see someone speeding. Thats why you still gotta keep your eyes open, dont just beleive the radar detector will work 100% of the time. Once the cop sees someone speeding then they can turn on the gun and BAM they got you.