Problem with alarm - triggered by light

[hmarsili]

Hi everyone,

I have a BMW 120i 2009. For the last past 6 months everything went perfect. A couple of days ago, the alarm started to trigger with no reason.

I took the care to the BMW Dealer and they informed me the ROOF volumetric sensor was the one activating the alarm. Pretty strange.

Important things:
1) this only happens in my garage
2) this only happens when my neighbor car arrives
3) talking with her, the alarm is trigger when her car's light are flashing at mine (the car always appears untouched)
4) the lights on the garage are pretty poor, so when a car enters, the light conditions changes a lot

The question here is: is this a normal behavior for the volumetric sensor or is the sensor failing?

I appreciate your help.

Regards,
Hernán.

[bowmang]

well, the sensor is a motion sensor... so i can see how this might be happening, but no... that is not normal operation, it seems like it is way to sensitive.

[hmarsili]

Thank you. The service already ordered the replacement part (15-days).

In an electronic forum I read that some volumetric sensors are sensitive to light-shades, so I wanted to be sure prior to the change.

[bowmang]

yup.. i've seen it before. it's pretty rare.. but is a very easy fix.

[hmarsili]

I was doing some testing. Today, I left the car with the volumetric sensor on BUT with the interior roof closed (before, I left the car with glass roof only).

No alarm triggered today, tested with 3 cars entering my garage... One of them, my neighbor.

What do you think?

[hmarsili]

Hi! I had the sensor changed. A couple of days later, some problem. The alarm is triggered whenever the neighbor car is parked and the sensor involved is the volumetric.

Any ideas? The pepple from BMW Service are kind of lost.

[randomy]

change the sensor back to the one that did not have this problem

[Cheyne]

Not being silly or anything, but I'm presuming that your neighbour doesn't have a stupidly loud bigbore exhaust or anything? My neighbour's Subaru STI used to set off my car alarm whenever he drove past because of the vibrations caused by his fart-can exhaust.

[hmarsili]

This is the second sensor BMW SERVICE changed. They thought the first one was malfunctioning.

If she parked the car in one maneuver everything is ok, but if she have to move the car around then the alarm is triggered.

The thing is not making any sense is the SENSOR INVOLVED: roof top volumetric sensor.