Glass Breakage Sensor: General: Function
WARNING: This page is about a different car, the 2002 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
When the anti-theft alarm is armed, the glass breakage sensor is activated when it receives a power supply +12V from the control module to pin 3.
If a window is broken, the sensor detects the sound, processes the information and decides whether or not to trip the alarm. If the alarm is to be tripped, pin 58 is grounded on the TWICE control module via pin 1 on the sensor.
When the key has been removed from the ignition, the glass breakage sensor can be deactivated with the NIGHT PANEL button on SID. Information on the deactivation is sent on the bus and is read by TWICE, which deactivates the sensor.