The button on the drivers side ultrasonic sensor housing is a "pet" button.
Pressing this button just before you exit the car and set the alarm will disable the ultrasonic sensors in the car's interior.
This allows you to lock and alarm the car while leaving a dog in there.
Fault codes can be read out of the Alarm by shorting pins A and H
(NOTE: ## on later models (?) this no longer works ????)
The code is flashed out on the ultrasonic led in the roof lining, passenger side
The Ultrasonic "pet" button clears the codes.
Fault with disarm signal
Boot caused an alarm condition
Bonnet caused an alarm condition
Doors caused an alarm condition
Ignition Turned on caused an alarm condition
Immobilization circuit open circuit
Radio caused an alarm condition
Ultrasonic caused an alarm condition
Fault with disarm signal. (central locking fuse blown)
Rear Window smashed caused an alarm condition ('92+ models only)
Horn Voltage Low ‑ Horn O/C or fuse blown
The immobiliser control unit has links to the anti theft alarm system. The immobiliser will not disarm if the anti theft alarm is active or has been triggered.