S1 alarm weirdness

[PZE]

As of this evening my alarm (2010 NA) has started going off 3 mins after locking. 2 strange things: it goes off very, very quietly (but doesn’t seem to stop) and it doesn’t turn off when I unlock the car and open a door. After pressing the lock button or putting a key in the ignition it stops. 

I’m blipping the alarm twice to turn off the microwave sensor so don’t think that’s the cause. Any ideas/experience of this? I know the battery is the default thing to worry about, but it’s fairly new and I think healthy - the car has sat still for 7-10 days a couple of times and started perfectly after that. 

[21gg]

This is going to sound very bizzare but try your horn! I replaced mine for a twin compact air horn, after its mot it started setting the alarmmoff after a few minutes very quietly. Took me a few days of thinking what they could have done during the mot, eventually found the horn fuse had blown. Still dont quite get how it effected the alarm but it did!

Gav

[Bibs]

This could be the battery in the siren, or of course your main battery. Check that first and if it's fine, you may need to replace the battery in the siren which means a new siren. 

[PZE]

Thanks both. @21gg I tried the horn as I drove away this morning and was more disappointed than I’ve ever been before on discovering a component working properly ... so sadly that’s not the fix. 

 

@Bibsthe siren battery makes sense in that it’s been getting progressively quieter on locking beep - although can you think of any reason that would cause the siren to trigger all the time?

 

[21gg]

When it's going off quietlt do the indicators flash, dont think mine did?  May be worth checking you're other fuses? Can you set it off deliberately and get full sound and indicators etc? Do the indicators flash when you set it?

Gav 

[PZE]

Indicators don’t flash while sounding. I’ve not tried setting it off properly, actually not immediately sure how (I suppose sitting in it with the microwave sensor on should do the trick). 

 

Indicators do flash normally with a very quiet beep when I arm it. Also get triple beeps correctly if arming it with doors open.

 

 

[21gg]

It sounds like its behaving almost identical to mine, definitely check your other fuses / things not working. Technically it shouldn't make a difference as the horn and alarm are completely separate circuits! The dealer hadn't heard of the issue before and their first thought was alarm battery, but in my case I knew it was something done during the mot which caused it.

gav

[PZE]

OK, I've had a chance to play with it some more after being away for the weekend, with these observations

• if I trigger the alarm deliberately it's also very quiet, but the indicators then do flash
• something I've never noticed before: when I lock it, the centre console button with a door/window icon (just next to central satnav display) lights up for a few seconds. Is this standard behaviour on an S1 or indicating a fault? Haven't yet found anything in the manual about it
• as long as I key-lock the passenger door there are no problems - alarm goes to 1.5 second flash and doesn't trigger

Sounds like a new siren battery to me, but would welcome any other thoughts before I try that.

[AK70]

The alarm system is a beast. My solution was, that I simply deactivated it by unplugging the siren cable. 
No problem since then.. ;-)

 

Lotus_Alarmanlage_ausbau.pdf

Edited March 28, 2018 by AK70

[AK70]

The alarm system remains active but without the sound of the siren.
A word of advice:  Please make sure, the alarm is  O F F  before you remove the cable... otherwise you will be deaf for a while..