A security system for preventing unauthorized removal of a vehicle accessory such as a radio from a mounted position on the vehicle comprises a dispensing container containing a pressurized protective material such as a pepper gas and having a dispensing valve displaceable from a closed position to an open position in which the protective material is dispensed from the container. A valve actuating member is responsive to displacement of the accessory from its mounted position to displace the dispensing valve from the closed to the open position whereby the protective material is dispensed from said container.