Abstract: There is disclosed a theft prevention system for trailers interacting with the customary pneumatic trailer braking system having spring actuated parking brakes that apply when in absence of pressure in an air supply line to the trailer from a tractor-mounted compressed air tank. A normally closed solenoid valve is connected in series with the pressurized air supply line that supplies air to release the trailer parking brakes and a signal receiver adapted to receive an electrical signal from a transmitter in the tractor cab must be caused to actuate the solenoid to open the valve to release the trailer parking brakes. The signal from the transmitter to the receiver may be a dc, ac, or high frequency signal transmitted over the normally provided electrical cable from tractor to trailer or may be a radio transmitted signal wherein of the kind employed for garage door openers.

Abstract: There is disclosed a theft prevention system for trailers with the customary pneumatic trailer braking system. A normally closed solenoid valve is connected in the line that supplies air to release the trailer parking brakes and a signal receiver adapted to receive an electrical signal from a transmitter in the tractor cab must be caused to actuate the solenoid to open the valve to release the trailer parking brakes. The signal from the transmitter to the receiver may be transmitted over the electrical cable from tractor to trailer or may be a radio transmitted signal . The solenoid valve is provided with a pneumatic latch so that the parking brakes will remain released as long as air pressure is provided. The signal transmitter is provided with security to prevent unauthorized use which may be a key switch, a key pad for entry of an identification number, a magnetic strip card reader or other device.