Alarm goes off on unlock

[wpeterso]

I have a 98 528i that has had some weird electrical issues. Currently when I lock the car with the remote or key the alarm goes off when opened...only after it sits for some period of time. If I lock it with the remote and then immediately unlock it it works fine. Does this indicate some sensor is bad?'97 M3 Bright Red

[540sport]

The alarm goes off if the voltage is low. Check the battery, charge it, check it again.
Vin
98 540 Sport with everything & extra hots
BMW CCA, Boston Chapter
"The 540 is the head-case supermodel girlfriend..." Eric S.
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[jimcash]

I agree with the other - it is probably that your main battery is low and is not fully charging the battery in the alarm unit.

Or the alarm unit itself is defective.

Is you main battery voltage holding above 12.4 after the car has been asleep for several hours?

Cheers
Jim Cash

[wpeterso]

Good question. Will check that. I read that the siren unit has a rechargeable battery. I assume you guys mean the car battery which is easy to check. May explain other squirelly electrical issues too (airbag light, etc.)'97 M3 Bright Red, '98 528i Black

[GHueser]

Just a longshot, but you may also want to check your Hood Switch for the alarm system. Disconnect it and see if the alarm still acts up. If all is well,(alarm is quiet),then you need a new switch.

[wpeterso]

I disconnected it Sunday with no joy. I also clicked the lock button twice to disengage the motion and tilt sensors...no joy. Haven't had a chance to check the car battery volatge.'97 M3 Bright Red, '98 528i Black