The DEI 504D Double Guard Stinger Shock Sensor can be added to the stock BMW alarm for about $10
The stock alarm only alerts to an external problem if the tilt sensor is activated as if someone is jacking up the car. If someone were to hit your car while parked, the alarm would not trigger.
The DEI shock sensor adds an adjustable sensitivity sensor that will trigger the alarm when the car receives a "thump". It connects with just three wires: +Pos - Neg and the trigger.
There are 4 wires. The blue and green are the triggers and provides a "warn" trigger (light thump) and an "alarm" trigger (heavier thump).
The stock alram does not support a "warn" trigger so we will tie the blue and green together.
I installed the sensor along with the stock motion sensor in the headliner. Remove the trim panel that looks like a "vent" - that is the motion sensor. Just pull down an edge and work it loose.
This shows the cable after I disconnected the panel
The wire diagram. We will use 1, 8, and 7
You need to tap into the power, ground and the blue trigger wire. The alarm is triggered when pin 7 is grounded - which is what the shock sensor provides. The blue wire goes to ground when a shock is detected.
I chose to scrape away the insulation and solder in the leads.
Completed sensor lead attached
I applied doublestick tape and attached the sensor to the roof panel. Hopefully this tape holds when it gets good and hot this summer. Place the sensor so that you can get to the adjustment screw.
Negative side effects to work out:
- If I lock the doors with the FOB when a door is still open - like with a passenger, the sensor activates the alarm when the door is closed.
- If the car is locked and alarm set, I can open the trunk. When I slam the truck closed, the sensor will activate the alarm.
So the stock alarm is smart enough to handle these situations but the alarm is active enough to allow this grounding trigger from the sensor to still activate the alarm. I will adjust my behavior to work around the limitation while I think on what to do about it.
** My first idea to check out: Pin 5 is supposed to be the lead that runs the LED on the mirror. I will check to see what voltage is on that pin before and after the alarm is set. It may turn out that the LED lead has power only after all the doors are closed and the alrm is active.