Why does my alarm keep going off for no reason?

[jamesdc4]

The first thing to check for in case of alarm falsing is a weak battery. If you don't have a voltage meter, you can do a quick and dirty test of the battery and charging system/alternator by unlocking the OBC and running test #9 in the list in either of the threads included in the second link below.
How can I tell if I have the High or Low OBC?
How do I unlock the OBC (Low and High)?

(Table image courtesy Qsilver7)

The next thing to check for is a bad hood sensor . I think this is probably the most posted reason for alarm problems. The interior motion and tilt sensors are also possible causes although I haven't seen many instances of these sensors causing the falsing.

Ditto ^^^ what others stated above about the hood, interior motion, and tilt sensor. It could also be a tell tale sign of a battery close to failing. You may want to check your battery's voltage which you can do if you've unlocked your OBC...run TEST #9 with the engine NOT running.

Try disconnecting the hood sensor...if that doesn't work...then turn off the tilt & interior motion sensor when you lock your car by pressing the lock button twice or turn the key in the door lock cylinder twice.

You can see where the hood sensor is located in the pic below...the electrical harness can just be pull off of it. After disconnecting it, lock the car as usual with the remote fob. If the problem goes away...then you've found the culprit. The hood sensor could be bad...or it could be that the insulation (on the hood) above the tip of the sensor has worn away.




Below are instructions from the owners manual on how to deactivate the TILT & INTERIOR MOTION sensors:

If it's not the hood switch, interior motion or tilt sensors, it could be your alarm siren.

It's not the hood sensor or interior motion sensor or tilt sensor or battery...
WTF is causing my alarm to go off?
I arm the system and when I disarm/unlock with key fob, the alarm sounds for 30 seconds and then goes off. When the alarm is sounding, I can start the car up with no problem (Gumbs will like that ). That is all.
Anyone have any ideas or come across this kind of problem?
Is it the EWS module?
I'm sick of closing the door, opening the rear door and leaning in to lock the car with the center console lock button.

Update on the alarm issue I was having. I changed out the alarm siren/horn (part #6 below) and the problem is solved. No more falsing.
If you are having alarm symptoms like I describe in the first post in this thread, this is the part you need to replace.

DIY for alarm siren replacement:
Alarm siren replacement

The way the alarm falses is a telltale sign of which of the above issues you may be experiencing.
(Special thanks to Qsilver7, Lon Leader, VietSB, and Peter Glaskowsky.)

[BlackBMWs]

I was going to ask you about this when you were going through this. So part #6 has a battery in the unit? Part #11 looks like a sticker.

Thanks!

[jamesdc4]

I was going to ask you about this when you were going through this. So part #11 has a battery in the unit?

Thanks!

Yes. It is a rechargable battery that loses its ability to hold a charge as it ages.

[jamesdc4]

Part #11 looks like a sticker.

BlackBMWs,

You're right. Part #11 is a sticker.
*fixed*

Thanks.

[Qsilver7]

I was going to ask you about this when you were going through this. So part #6 has a battery in the unit? Part #11 looks like a sticker.

Thanks!

BlackBMWs,

You're right. Part #11 is a sticker.
*fixed*

Thanks.

Fellas...if you all are referring to #11 in the diagram below...that's not a sticker...the little triangles in the diagrams are electrical sockets (harnesses/connectors)...see #12 & #13, they are also electrical harnesses.



Item #11 in the diagram above...is the electrical connector seen circled on the far right in the pic below from the write-up on how to change the siren:

[jamesdc4]

Ahhhh.
Thank you, Q.

[LuisGT]

What if it's non of those three?

I dealt with this for a couple of months, started a month before my GM3 module died, and it kept happening with the dead module, somehow I managed to revive the module and it fixed the alarm going off 30 seconds after locking the car, haven't had a false alarm since.

just my 2 cents

[jamesdc4]

What if it's non of those three?

I dealt with this for a couple of months, started a month before my GM3 module died, and it kept happening with the dead module, somehow I managed to revive the module and it fixed the alarm going off 30 seconds after locking the car, haven't had a false alarm since.

just my 2 cents

Those three things in the first post are the most common reasons for alarm falsing, but certainly not the only ones.

[cal45fan]

I did this not too long ago and it was a success!

[BimmerM3inGA]

Has anybody tried to crack it open and just replace the battery instead of the whole thing?

[jamesdc4]

Has anybody tried to crack it open and just replace the battery instead of the whole thing?

I haven't heard or read about anyone trying it. I have my old siren in the garage. Let me take a good look at it and see if i can open it up without destroying it. If it can be opened, I'd assume you could replace the rechargable battery.

[jamesdc4]

Okay. I tried to open it but had no luck. It looked promising at first, but I couldn't get past removing the three screws. I even tried a hammer to get it open. Apparently it's sealed.










Edit: I read a thread where a member claims he replaced the rechargable battery. If I can locate the thread, I'll post it here.

[BimmerM3inGA]

Dang! Looks like I'm buying a siren. I'll just add it to the list.

Thanks for giving it a try and posting the results.

[kingsly]

SO can anyone explain why my alarm only goes off for no reason when the car is parked at my mom's house?

No joke.

[Qsilver7]

SO can anyone explain why my alarm only goes off for no reason when the car is parked at my mom's house?

No joke.

How about some details or context? There have been suggestions already presented...if you've tried those and can eliminate them as suspect...let us know so that we don't have to keep repeating the same thing over again.

The 3 common problems are:

1. car's battery affecting the alarm's battery
2. turn off the interior motion and tilt sensors
3. disconnect the hood alarm sensor

Have you eliminated any of those 3~4 things as the culprit? Are there small kids or other people that may be leaning or bumping the car (intentionally or unintentionally), does she live on or near a busy street that may have vibrations from large vehicles passing by?

How long is your car parked at your mom's house...are you storing it there...or are these short visits?

[kingsly]

Short visits, sometimes parked on the street and sometimes in the mostly flat driveway. I've even had it go off when parked on the next block over. Very quiet street, not really any kids or pedestrians of any kind (as the song goes, nobody walks in L.A.... ) and no cats. It's literally never gone off anywhere else I've parked it, including my fiancee's house where there are horses galloping up and down the street, mine where the neighborhood stray uses the bonnet as a bed, or at the airport 15 feet from a hovering helicopter...

I'm starting to think there's a mystical magnetic field by my moms house that my car isn't fond of!

[edjack]

kingsly,

Look around the 'hood for a ham operator, or proximity to a radio or TV transmitter.


BimmerM3in GA,

Mine quit chirping. Replaced it, and cut the old one open (they're sealed). The battery was okay.

I did lose the wolf whistle, and the new one sounds like a Camry.

[jamesdc4]

BimmerM3in GA,

Mine quit chirping. Replaced it, and cut the old one open (they're sealed). The battery was okay.

I did lose the wolf whistle, and the new one sounds like a Camry.

What method did you use to cut it open?
Was the siren destroyed by cutting it open or were you able to get it open in a civilized manner affording you the ability to glue it back together?

[2001 530i Sport]

I will try suggestions in this post over the weekend. My alarm goes off any time from 1min to 4-5hrs after I have locked the car. No reason for it to go off.

Thanks,

[mortonkd]

I just started having this problem today. I disconnected the harness to the sensor and will see how that goes. Can I get a new sensor from an auto parts store or is it strictly a dealership part?

[BimmerM3inGA]

FWIW: I unplugged the switch under the hood (next to the driver side cabin filter housing) a few months ago and the problem has not returned. Is that the sensor you're asking about? If so, it's probably going to be a dealer part - but it's not the problem. The problem is the siren itself. Or, more specifically, the rechargeable battery inside it.

[alpinweib]

i just pulled the fuse in the trunk. now my alarm doesnt go off randomly and my car doesnt chirp when i lock or unlock it.

[jamesdc4]

i just pulled the fuse in the trunk. now my alarm doesnt go off randomly and my car doesnt chirp when i lock or unlock it.

Essentially, your alarm doesn't work. Great for silencing the problem but not for fixing it.
The chirping is a memory option that can be turned off/on by the dealership service dept. or anyone with the proper software, cables and a laptop computer.

[Cyrix2k]

i just pulled the fuse in the trunk. now my alarm doesnt go off randomly and my car doesnt chirp when i lock or unlock it.

seems like a good solution to me. Since when has an alarm helped anyone recently? If anything, it will probably get the car vandalized when it's set off.

[mortonkd]

FWIW: I unplugged the switch under the hood (next to the driver side cabin filter housing) a few months ago and the problem has not returned. Is that the sensor you're asking about? If so, it's probably going to be a dealer part - but it's not the problem. The problem is the siren itself. Or, more specifically, the rechargeable battery inside it.

I unplugged the switch today and the car has been acting fine since. It has been silent for the rest of the day. So that has me to believe it's something with that sensor. I shouldn't have to buy a whole new siren for just that part correct? The car still chirps when I lock and unlock it btw.