About the size of a conventional automotive key, the Check Module is the testing portion of the ignition lock system. The Check Module is easy to attach to one's key ring. This device is much easier to operate than, for example, a breathalyzer analysis device; it is a bit like playing a 2½-second video game. As further built-in security a given Check Module only communicates with a unique and individual code only with the interlock device specifically installed in the vehicle.
This component prevents the car from being started if the Check Module test is not passed. In order to start the car, the Immobilizer must receive a positive command from the Check Module. The Immobilizer is a reliable solid-state electronic circuit that is professionally installed in the vehicle, typically under the dashboard. Again, this device can only be commanded by the single corresponding Check Module.