Bad weather sets alarm off

[Geoff1951]

Morning all. I've seen the several threads on alarm problems but not quite had this covered, as far as I can see. Three or four times over the past few years, when there has been a sudden torrential downpour - usually hail - and not too windy - the alarm on my nearly 8 year old ('54, Jan 05) 95 has gone off. Always at night.    . The car is parked outside on the driveway, not garaged.

It's now done it five times in the past few days, to the extent that last night I had to leave the car unlocked. We have had some really heavy and sudden rainstorms, but not particularly windy.

Doesn't trigger if I try rocking the car (not easy, esp. with Hirsch suspension) and is only triggered by sudden rain/hailstorms

Is it the module/battery in the wheel arch, or the tilt sensor (which I'd prefer it to be, since I understand it's inside, under the driver's seat!)

Or something else? Over to the experts...

[ScarbSaab]

It's the glass break sensor. These use microphones and look at the shape of the waveform. I've been at a dealership when hail started and to have a dozen 9-5s suddenly going off is...loud.

EDIT:

Just a thought - rather than leaving it unlocked you should be able to use the doors only mode - press and hold the night panel button just before you get out of the car.

[Geoff1951]

Thanks ScarbSaab. Is there a cheap cure?

[sgould]

Hail will set off the glass break sensor alarm.  Strong wind can set off the tilt sensor alarm. You can disable the glass break sensor and tilt sensor by pressing the Night Panel button as you leave the car.  Instructions in the handbook.  Can't remember if you do this before or after removing the ignition key.  SID will say "Doors only alarm".  The alarm will go off if the door, boot or bonnet is opened.

I've not heard of a glass break sensor failure.  Tilt sensors on early cars could go faulty and set off random alarms. Glass break sensor is in rear roof light.  Tilt sensor is under driver's seat.

But on an 8 year old car, the random alarm is more likely to be failing batteries in the alarm box.  Do you get a "Service theft alarm" message on SID when you turn on the ignition after the alarm has gone off? If so, it will almost certainly be the batteries in the siren box.  Maybe the condensers as well.  But the main clue to this is if the alarm still goes off when set to "doors only".

Boxes can be repaired.

www.saabdisplayrepairs.co.uk

www.sidmaster.co.uk

[Norfolk Jim]

Geoff - mine does exactly the same and is 55 Reg.

It happens if very heavy rain or hail of which we've had both recently. I'm glad I'm not the only one!!!

Don't think its the alarm batteries as it is only during this bad weather. All other times it is silent.

I will look at pressing Night Panel and see if it stops it! Just hope no-one tries to break in through the glass at night. It's possible using the ceramic on a spark plug and happens silently!!!!!

[sgould]

I live between the High Street pubs and the former council estate.  The estate was a bit of a time bomb.  It was built opened all in one go and filled with young couples.  So 17 years later there were gangs of kids, all the same age with illegal mopeds and into underage drinking.

We got a bit of vandalism for a while.  But there were a couple of "clever" lads who fancied stealing a car up the road.  So, every time they came past on the way back from the pub, they threw handfuls of gravel at it until the glass break sensor alarmed.  After several of these alarms and complaints from the neighbours, the owner switched the alarm off...........

[collywobble]

Ours always goes off in heavy rain or hail - you would think they get a bit of hail in Sweden - or perhaps it only ever snows!

N.B. to me:   Must train SWMBO to set to doors only so I don't have to get up at 2.00 am in the morning to do it myself!

[ScarbSaab]

Personally I've not been bothered by it except on a few occasions when it has gone off in the night. Most aggravating is when you go to the window, press the button and just as you've got comfy again, the hail resumes.

I wonder if one of those car covers would soften the impact so it didn't trigger?

Alternatively, if someone looks at the wiring of the glass break sensor you might be able to bypass it. Probably not as simple as shorting the alarm wires on a domestic sensor, but if the microphone can't hear anything...

If anyone has one from a breaker it could be worth investigating how it operates.

[Audax]

To disable the glass break sensor you can hold down the night panel button when the key is out of the ignition and it'll cycle through the alarm options available and let you set the alarm to "doors only" but you have to to this each time you leave the car. To bypass them entirely you just unplug them, TWICE will log a fault code but it won't activate if they are not there but you'll get a "service theft alarm" message on the SID. You can bypass that with Tech-II

[Geoff1951]

Thanks to sgould, Norfolk Jim, collywobble, Audax and again ScarSaab. From what you've all said it's definitely the glass break sensor. I'll check the handbook for the exact night panel button procedure. Car is safe enough on the drive, SWMBO's Peugeot is parked in front of my 9-5, and there's nothing of value in either. And we're a bit off the route of the local scrotes, thank goodness. Just the odd chip paper 100 yards down the road at the lights.

IMHO if the glass gets broken regardless of the sensor that's enough aggro. Anything else is minimal. 

A pity the weather doesn't give advance notice of sudden downpours...

[sgould]

I wonder if you can open the glass break sensor cover and stick an earplug in it?

[Geoff1951]

LOL, as Rebekah Brooks would say!

[sgould]

Item C is the sensor in the centre roof lamp of the saloon.

There's a second sensor in the rear roof luggage lamp in the estate.

[Geoff1951]

Thanks Will! You weren't joking!

[sgould]

I was thinking last resort!!

But it might work.....