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Stan, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3526
Experience:  Technical support engineer
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My car alarm went off, I think because my battery was flat.

Customer Question

Hi, my car alarm went off, I think because my battery was flat. I couldn't stop it and disconnected the battery terminals. A secondary alarm continued but faded out eventually. I've charged the battery but when I try to reconnect it - it just sets the alarm off. My car is a 2002 A140 Avant Gard. Can you help please? Sue
Submitted: 2 years ago.
Category: Mercedes
Expert:  Stan replied 2 years ago.
Hello Sue,
Such symptoms indicate that the rechargable battery in the alarm's siren has failed and needs to be replaced. Alarm system sees that the failed siren is missing, so alarm is triggered.
Siren is hidden well under the wiper mechanism.
Let me know how i can help you more on this
Best Regards,
Customer: replied 2 years ago.

What does the siren look like, where do I get a replacement battery from and if the battery has failed what I powering the alarm? Thnks,

Expert:  Stan replied 2 years ago.
The battery in the siren is not replaceable separately- so complete siren must be changed. It looks like a black black box, but you will not see it untill carbon air filter is not pulled out and wiper system partially disassembled.
When the siren does not communicate with the alarm system, alarm is feeding the siren directly from the battery. Now faulty siren continues to run from it's weak battery once the main battery is disconnected. Properly working siren would run off it's battery for hours after main battery has been disconnected.

You can get the siren from Scorpion alarm company: