Alarm Siren Problems
 

I have a 2000 2.5 Boxster. It has suffered all the usual Boxster ills, leaking hood, flooded BCC computer, squeaky ball joints etc. All have been fixed over the last 7 years of ownership and I am still in love with it!!!

The latest issue was the alarm kept going off, it double beeped when setting and it would only turn off if the battery was disconnected.

In desperation I took it to a local garage and they diagnosed the alarm siren back up battery was dead causing the the alarm to believe it was being tampered. They solved the problem by disconnecting the siren. It seems that new sirens are no longer available and they pointed out that a second hand one would be likely to have the same weak battery.

So is there any way to replace the back up battery, has anyone tried to do this? I haven't tried to do anything to it yet, in fear of upsetting the rest of the alarm!

https://986forum.com/forums/performance-technical-chat/35081-battery-alarm-problem.html

Do you have option M534?

"Vehicles for the UK and Belgium are equipped with an alarm siren and a tilt sensor in addition to the standard alarm system. The M 590 (locking system for the bonnet controls) is also fitted as standard."

Check https://www.porscheclubgb.com/forum/threads/alarm-developed-a-life-of-its-own.143723/ also

I would try to get a new battery from https://www.hamilton-palmer.co.uk/. Alternatively, I would try to disassemble the old one first to see the specification of battery.

9x6 cars don*t have an alarm siren with an integrated battery.

Double beeping when setting is in general a hint that the alarm ecu is faulty.

Check for another workshop with people who know what they are doing.

Double beep in my case was the result of a faulty ignition switch. Cheap and easy place to start...

Unfortunately, British market 986's did come with an independent alarm siren that is powered by its own battery. From a British Boxster board:

"The alarm siren has its own battery. As the siren battery recharges from the main battery when the main battery goes flat the alarm siren battery will discharge. When it discharges the alarm siren goes off as the alarm system 'thinks' it's being interfered with. It will repeat sounding until it no longer can.

You could pull the electric plug from the alarm siren which will silence it but then its independent battery won't recharge."

Somewhat related but not really. I have an issue where when i attempt to lock the car from the door, it double beeps and instantly unlocks itself. It recently started happening, my first guess would be something on the door as it was taken apart to do window regulators not long ago. Could something be unplugged or have gone bad through that disassembly ?

Another note, it locks just fine when im inside and press the lock / unlock on button next to the radio so im wondering if its on the driver side door. Potentially a switch?

Ups, you're 100 % correct.

The alarm horn is 996 637 117 03
The alarm siren with integrated inclinometer is 996 618 237 04

Never had a 9x6 car with an alarm siren system in my workshop.

Over here in Germany we have lots of other cars with alarm sirens that fail because the batteries leak. You can try to open the housing and take a look how much damage the acid has done. I could save some of the modules by removing the batteries and resolder the pcb lines. But that's more of an amateur approach as the siren will only work when the main battery is connected. Sometimes components are toast. And you really need some electronics and solder skills.

Attached you'll find some pictures of a mercedes alarm siren module that now works again - without batteries.