The engine immobiliser is disarmed automatically when you switch the ignition on with a correctly coded key.

The indicator in the instrument cluster will come on for approximately three seconds and then go out. If the indicator stays on for one minute or flashes for approximately one minute and then repeatedly at irregular intervals, your key has not been recognised. Remove the key and try again.

If you are unable to start the engine with a correctly coded key, this indicates a malfunction. Have the immobiliser checked immediately.