Car battery / false alarm trigger?

No I don't think its what is wrong. They have an internal battery, when it gets weak the alarm starts to beep and eventually starts to do odd things. The battery is in the sounder which may be under the wing behind the arch cover as on my Astra. The unit is sealed but you can split it and replace the battery pack, I just fitted a new unit. There was no need to pair it to the rest of the alarm but YMMV.

hot temps causing thermals in car drawing air thru heater vents being detected by interior sensor? (or similar) close vents and see if it works - does on our Toyota...

Cheers Jim K

No. If it can start the car, it can feed the tiny current the alarm circuit needs at the full 12V. Also, the alarm electronics are likely to be fairly tolerate of variations in the supply voltage.

My Touran pulls this stunt once in a blue moon. I blame the internal PIR sensors... But that's very hypothetical as there's no way I can test it as such.

In message , Lobster writes

Sunshine causing micro-switch to trip (bonnet or tailgate?)

regards

It doesn't have a volumetric alarm, does it?

Fly trapped inside?

That was my instinct as well. I always shut my climate control down by hitting the recirculation button, so that any air that is in the car can't get out, or blown around for the IR sensors to trigger the alarm.

Dave

Bit unlikely - the alarm microprocessor likely runs off a stabilised supply of probably 5 volts.

If it is a decent one it should be accurate.

Can you switch off some of the alarm sensors? On many you can put it into 'tow' mode which disables the movement sensor and perhaps an interior sensor? Check the handbook. An interior ultrasonic sensor can be upset by slight glass etc movement if the sensitivity is too high.

On my getting ancient BMW, the fresh air etc vents for the climate control all shut when you switch the ignition off.

while parked up, for no apparent reason.

(as these days it is mostly used for short journeys

charge some weeks ago) and consequently the alarm goes

original battery (~7 years old).

several hours); but I had no difficulty in starting

offers 'free battery testing'; bloke attached a

battery, and the thing came up with "Good battery"

check or test? Otherwise is it a trip to the

alarm/immobiliser?

Passing powerful radio transmitter in a taxi / police car / fire engine / radio ham etc.

I have seen this many times but to be honest it used to be more prevalent 15 or

20 years ago. Furthermore, I would like to think that any factory fitted accessory would be immune to this kind of thing, with all the EMC regulatory requirements on modern vehicles.

Don't rule out the possibility completely though.

In article , Lobster writes

I had exactly the same problem with my Zafira last year.

The alarm system has a separate battery unit located under the front drivers side wheel arch which operates a sounder if the cars normal battery is tampered with. This 'alarm' battery unit loses its charge after several years and operates the sounder spontaneously.

Only cure is to get this 'alarm' battery unit replaced or take it apart and see if you can replace the individual batteries. I took the easy option and had the whole unit replaced as a local firm specialising in car electronics had a unit in stock.

I don't know if Vauxhall changed the system on newer Zafiras; mine's an

02.

Thanks to all for the replies - does sound like the above is the most plausible.

Re other replies - I don't believe it's a climate-control thing as it's been happening with the car cold and unused. And although I'm sure it has in the past very occasionally been triggered by a passing juggernaut etc, that wasn't the case last time as it was during a quiet late Sunday evening (I particularly remember the 'quiet' bit as I dashed outside to sort it out!)

Thanks David

I told you that two days ago.

I suspect Lobster, as have many others here, placed you on their killfile list.

It smacks to me of poor design. I have an aftermarket alarm on the old Rover with a battery backed up siren. The only reason for that is it goes off if the car battery is disconnected - or the feed to the siren or alarm interfered with. It has a key to disable this function. So why that internal battery failing would cause it to sound - if the main one is good

- I dunno.

Well if they choose to believe the idiots that say I am wrong then that's their hard luck.

Yes, you posted that last night and I'm grateful - I logged on this morning and read all the replies together. No offence was meant by not following up your post rather than Peter's I can assure you.

Incidentally I'm now 100% sure this is the problem, as since googling for 'power sounder' I've discovered that it gives a warning before failing of 4 beeps as you turn the engine off. My car's done that occasionally over the past year(!) but I hadn't put two and two together. People are saying these power sounders only last 2-3 years so I've done pretty well on 7 years it seems. I phoned the Vauxhall dealer about a replacememt (£75) but they'e sold out today (a 'very good seller', he says. No kidding... what a load of bollocks.

David

They are tagged 1/2AA cells IIRC. You can split the mouldings and replace them, but its difficult to reseal the plastic. I got my replacement at a discount and it didn't cost any more than the cells would have.