This key ring sized device can detect the power transmitted by the cars immobilizer system. This can be useful in diagnosing system faults or checking to see if the car is immobilizer equipped. If there is no emitted signal it will help narrow the fault tracing path. There is no need to try programming a new key or component if the aerial is not working. To use, hold it beside the ignition key against the outer edge of the ignition lock as you turn on the switch. If the system is working, the bright L.E.D. light will illuminate when the immobilizer coil powers up to read the transponder key.