This is the H.A.R.D. System shown in the picture below. The quarter in the picture gives you an idea of how small the components are.

You can see the transmitter in the top of the first picture. The transmitter unit plugs into the radar detector (not shown in the first picture).

You can see the receiver in the bottom of the first picture. The receiver has the red LED indicator which is the visual alert that you see in the helmet.