The purpose of a radar detector is to detect the invisible radar waves in the air that are used to get a speed measurement of your vehicle. When a radar detector encounters the invisible radar waves, it will give you an audio and visual alert so you can decide what to do with that information (for example, you can slow down!). Used properly, a radar detector can be a very powerful tool for not only preventing speeding tickets, but for being aware of other radar-emitting hazards on the road ahead such as construction zones, law-enforcement officers, and EMTs rendering aid to other motorists.