W211 2007 alarm going off randomly.

[boxer 01]

The alarm on my w211 has been going off when parked outside my house on a busy road, this has started happening only recently. I don't park on the main road very often because of parking restrictions but when I've parked somewhere with less traffic going past the alarm doesn't go off, from what I've been reading if the batteries in the siren are going the alarm should be going off randomly no matter where I park. Is the sensitivity on alarm adjustable or is the unit on its way out, bear in mind the car is 17 years old and still on the original siren unit.

 

[DSM10000]

Almost certainly a failing alarm.

The battery in the alarm is rechargeable but eventually it fails to hold charge and will be behave as yours is

You can disconnect and remove it without any problem. It is usually behind the left wheel arch liner

 

[ALFAitalia]

Sounds to me like its over sensitive (like many members on here!!) and its being triggered by the vibration/noise of passing traffic. If it was anything else it would go off all the time rather than just when parked on the road. I'm afraid I've no idea if its adjustable though.

I used to haven open piped, pretty much full race, Suzuki GSXR1100L I used on the road back in the mid 90s.....it used to be able to set off car alarms in parked vehicles as I rode by!!

 

[MSG2004]

It may not be the case, but any spiders in there?
Spiders have triggered our conservative alarm in our previous house but that was over 17 years ago and possibly car infra ed beams are not as sensitive.

 

[AMGeed]

If you do disconnect and/or replace the alarm siren, it should be found behind the o/s/f wheel arch against the bulkhead. At least, that's where mine was situated on an 04 W211.
A new one is plug and play, no probramming required. An easy DIY job.

 

[markjay]

Almost certainly a failing alarm.

The battery in the alarm is rechargeable but eventually it fails to hold charge and will be behave as yours is

You can disconnect and remove it without any problem. It is usually behind the left wheel arch liner

This is the most likely explanation.

The other option is a loose or faulty bonnet/boot/door sensor.

 

[boxer 01]

Thank you all for your replies, I shall be checking all sensors soon, but it's only doing it when on the busy main road, it's none gone off since I posted as I have been parked elsewhere where there is not much traffic.
Alarm units aren't cheap either approx. £150.

 

[OneForTheRoad]

Thank you all for your replies, I shall be checking all sensors soon, but it's only doing it when on the busy main road, it's none gone off since I posted as I have been parked elsewhere where there is not much traffic.
Alarm units aren't cheap either approx. £150.

Just disconnect it , no one takes any notice anyways .

 

[DSM10000]

Thank you all for your replies, I shall be checking all sensors soon, but it's only doing it when on the busy main road, it's none gone off since I posted as I have been parked elsewhere where there is not much traffic.
Alarm units aren't cheap either approx. £150.

I would not be replacing it , I would be removing it.

Plus, you don't know it is the alarm unit and not a sensor.

 

[OneForTheRoad]

Just disconnect it , no one takes any notice anyways .

If money is an issue , look on eBay for a used siren .

 

[boxer 01]

I would not be replacing it , I would be removing it.

Plus, you don't know it is the alarm unit and not a sensor.

If I remove it will it not cause any other time issues with the car. Would the car lock normally with fob just the siren wouldn't sound if someone broke in. I'm going to plug into my scanner later and see if any faults are logged regarding the alarm.

 

[DSM10000]

If I remove it will it not cause any other time issues with the car. Would the car lock normally with fob just the siren wouldn't sound if someone broke in. I'm going to plug into my scanner later and see if any faults are logged regarding the alarm.

I removed the alarm from my W203 without issue. It cannot have any effect on locking etc.

When was the last time someone broke into your car and do you really think an alarm is a deterrent?

 

[OneForTheRoad]

If I remove it will it not cause any other time issues with the car. Would the car lock normally with fob just the siren wouldn't sound if someone broke in. I'm going to plug into my scanner later and see if any faults are logged regarding the alarm.

If it's not the siren at fault and the alarm is triggered by another source, I'd imagine your indicators will still flash . Is this the case ??

 

[boxer 01]

If it's not the siren at fault and the alarm is triggered by another source, I'd imagine your indicators will still flash . Is this the case ??

What's been happening is audible alarm has been sounding with lights flashing then the it stops sounding and lights keep flashing till I unlock and lock again. I've just scanned but no fault codes for alarm logged.

 

[OneForTheRoad]

What's been happening is audible alarm has been sounding with lights flashing then the it stops sounding and lights keep flashing till I unlock and lock again. I've just scanned but no fault codes for alarm logged.

Sorry, I meant if you remove the siren , and the alarm is still triggering will the lights flash. This will prove that it's not the siren at fault. Tbh a 2007 siren will be at the end of life by now.

 

[boxer 01]

Sorry, I meant if you remove the siren , and the alarm is still triggering will the lights flash. This will prove that it's not the siren at fault. Tbh a 2007 siren will be at the end of life by now.

Ok, I'm just going to leave it for now as where I usually park it's not going off and if it does get worse I'll unplug it and maybe find a replacement at a reasonable price. Thanks everyone.