Faulty Alarm on Mercedes

[Llonaid]

I have developed a faulty alarm on my 1998 Mercedes C220 Diesel Estate.
My alarm has recently decided to go off for no apparant reason at the most inconvenient times, (usually in the middle of the night). I have tried to disarm the wretched thing by unlocking the car, but within a very short while, the car re-locks itself and the damned alarm starts shrieking again. To say the least I am begining to become rather unpopular with my neighbours.
Can anyone suggest how I might rectify this problem or at least disarm it.
Many thanks

[Barmaid]

Have you got a "towing" option on it. If you press the button before you lock the car, it disarms the alarm. Quite useful on ferries, i discovered.

[R1Geezer]

It's the siren backup battery that's knackered, mercs are known for this, if the siren backup battery is gone then it goes off whenevr it feels like it. New siren needed.

[Llonaid]

Hi R! Geezer, Thanks for your answer, but would the back-up battery problem cause the doors to re-lock themselves when the key is out of the car?

[R1Geezer]

not sure about that but the whole lot is interconnected, give this lot a call, search for StarTech in Poole, I had similar trouble and these guys are the experts.

[Llonaid]

Many thanks for your responses. I will be ordering a new siren.
Thanks again to you both.