Alarm Siren
The alarm siren is mounted in the rear wheel well, behind the inner wheel housing cover (early E38 used an alarm horn). The E53 alarm siren is located in the left side of the engine compartment.
The siren contains electronic circuitry for producing the warning tone when the alarm is triggered. The siren also contains a rechargeable battery that is used to power the siren when the alarm is triggered.
The rechargeable battery will allow the siren to sound if it or the vehicle's battery is disconnected. The siren battery is recharged, from the vehicle's battery, when the alarm is not in the armed state.
The siren has four wires connecting it to the system; KL 30, KL 31, activate siren signal (SIRENE) and the arm/disarm signal (STDWA).
The arm/disarm output signal from the GM is provided to the Tilt sensor, FIS/UIS sensor and the siren. The arm/disarm signal is a switched ground that signals the components of an armed/disarmed status.
The activate siren signal to the siren is high whether DWA is armed or disarmed. If a monitored input activates the alarm, the high signal to the siren is switched to a 50% duty cycle at the GM. The control circuitry in the siren activates the siren driver.
If the DWA is armed and the battery is disconnected the siren recognizes the normally high "SIRENE" signal as suddenly going low, the siren is activated.