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Discussion Starter #1 (Edited)
I wonder if the good people here can help me (and my neighbours') sanity?

After a period of being laid up while I was out of work I'm now readying my 840 for a new MoT and treating it to new tyres, wheel refurb and one or two other items to make it legit again.

Anyway, to cut to the chase I'm having alarm problems and have been for a couple of weeks now.

One of the old batteries was knackered, wouldn't hold charge and so I've replaced both batteries with new but in the last week before changing the batteries the alarm starting going off.

I thought maybe it was something to do with low voltage but the alarm sounding off has continued since installing the new batteries.

It is not going off continuously but periodically every couple of days and always at around 1:30am - 2:00am when it wakes me (and probably some neighbours too).

Unlocking the car stops it as it you would expect and relocking it resets everything, usually okay but sometimes it will sound off for a second time during the night. When that happens I leave the car unlocked until the morning (it is safe, locked in behind one of our other cars).

Locking it again the next morning it will be okay for a night or two until it sounds again in the wee small hours.

The car is sheltered under a car port so is not exposed to the weather or strong winds to rock it, similarly no-one can access it to set it off without our security lights going on.

Why it has suddenly started doing this I don't know but it is intermittent but I could do with some pointers into where the problem may lie.

Thanks for reading this far and any suggestions gratefully received.
 

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You might have new batteries - but do they have any charge in them? The alarm will sound once if the battery voltage drops below a certain threshold, best get a meter on the batteries, or give them a 24-hour charge.
 

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Discussion Starter #3
Hi Timm,

Thank you for your reply.

When I installed the batteries last week I gave them a 36 hour charge and after removing the charger that evening the alarm went off again barely six hours later. The batteries shouldn't have discharged that much in such short time to drop the voltage low enough.

I'll put a meter on the terminals again tonight to check the voltage, am I correct in saying the alarm sounds when the voltage drops below 12.2V? I'm sure I read that somewhere.
 

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My alarm started playing up about 6 months ago however if I lock it with the key it is ok, alarm only goes off if set with the remote.
You may have the same issue?
 

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Discussion Starter #5
I've just put a voltmeter across the terminals under the bonnet and have 12.95 Volts. This is a week now since it was charged and it has been started four or five times (but not taken out for a run) since last Tuesday.


Lock with the key? Thanks Terry, I'll try it and see what happens.
 

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Discussion Starter #7
Latest update:

I've left the car for a couple of days completely undisturbed and all was okay until this evening. The car hasn't moved, hasn't been touched, nothing and no alarms for three days - until about 10 minutes ago.

I've checked the batteries and the voltage at the terminals under the bonnet was 12.65V.

I don't get how it sits quiet for days and then goes off randomly.

On the plus side though at least it wasn't 1:30am.

Looks like I'll have to check the bonnet switch and heater element this weekend.
 

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Hi Slotter

I read a few posts and threads about the alarm itself playing up.... its fitted with small back up rechargeable batteries that faill over time.

Guess the idea is alarm keeps going if someone disconnects main car batteries.

Its fitted under front scuttle drivers side.

I'll see if i can find the threads.


Cheers
And
 

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Discussion Starter #9
Hi Ferni,

Thanks for your reply, that sounds feasible as the car was laid up for some months with the main batteries dead so it follows that alarm batteries would also have run out of juice in that time. If they were getting on a bit then maybe they couldn't recover.

I'd be interested in those threads you mentioned but a search so far has proved fruitless.
 

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Hi Slotter

I cant find them either. In the thread i was thinking of the guy guy hacked the back off the alarm unit and all the button batteries were all corroded with plenty of green crust all over the circuit board.

Heres one thread but it is a different problem to yours.

Alarm Siren Replacement

Still sounds likes Timm's suggestions are more likely.... that rear window defogger comes up a lot in threads as does the bonnet switch

Best to test them out before firing the parts cannon.
Good luck

And
 

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Discussion Starter #11
Update:

The bad news is that due to having some very busy weekends I haven't got around to checking the heater element or the bonnet switch.

The good news is that it is now three weeks since the alarm went off. The new batteries are, as they should be, holding their charge, and the car has been started numerous times without running the batteries down.

So whatever the alarm gremlins were they appear to have disappeared. Result!

Thank you all for your help. :thumbsup
 
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