The 173 ppi transponder immobiliser is an effective two circuit system which arms automatically 30 seconds after the ignition is turned off. This system is totally unobtrusive - The only visible change is a small flashing LED fitted to your dash. You will have a plastic fob on your key ring that contains a uniquely coded transponder that is sensed by a toroidial coil that is hidden (usually) behind the steering column. On entering the vehicle, the presence of the key fob is detected by the coil, and the immobiliser is disarmed. On leaving the vehicle, the immobiliser is armed automatically 30 seconds after turning the ignition off. You need make no effort at all, Just get in the car, turn the key and away you go - no fiddling with sensor pads or inputting codes each time you want to start. The control unit is housed in a tough, polycarbonate housing in a secure location behind panels requiring tools to remove, thereby deterring the opportunistic thief, and even should the thief find it, all the control wires are plain black in colour making the tracing of their functions all but impossible.