C5 X7 ALARM when battery disconnected

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mitsub
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C5 X7 ALARM when battery disconnected

Unread post by mitsub »

I've followed the BSI Reset/ Battery Disconnection / Reconnection but now when I remove the battery negative lead the alarm sounds and will only stop when I reconnect the lead back and use the remote to silence the alarm.
I've had the car 3 years and done the procedure many times, to charge the battery, install new radio etc. In fact I didn't know I had an alarm!
Any ideas?
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mickthemaverick
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Re: C5 X7 ALARM when battery disconnected

Unread post by mickthemaverick »

That intrigues me, if the alarm sounds when you disconnect the battery then it must have its own power supply, presumably a battery inside. In which case you could stop it happening by removing the battery since you didn't know you had an alarm you won't miss it? :-D
I used to be indecisive, now I'm not so sure!
I used to ride on two wheels, but now I need all four!
PaulC5
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Re: C5 X7 ALARM when battery disconnected

Unread post by PaulC5 »

I believe the siren will have a back up battery in it.
mitsub
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Re: C5 X7 ALARM when battery disconnected

Unread post by mitsub »

I believe the alarm is working as it should do. I lifted the bonnet and the alarm went off, using the remote stopped it, removing the negative lead set the alarm off with remote stopping it. That is not supposed to happen as I have done it every time following the instructions form this forum. Is there a procedure to disable the alarms completely. It might have had it applied before I bought it. As last year I had a new injector fitted and vacuum pump installed by the local garage.
The car battery has to be disconnected to install a new radio.
wheeler
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Re: C5 X7 ALARM when battery disconnected

Unread post by wheeler »

The alarm should only go off when disconnecting the battery if the alarm is armed at the time when it is disconnected.
mitsub wrote: 20 Mar 2026, 12:11 The car battery has to be disconnected to install a new radio.
Officially probably yes it does but in reality i would never bother for installing a radio.
ozvtr
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Re: C5 X7 ALARM when battery disconnected

Unread post by ozvtr »

The alarm should only be active when the car is locked (with the fob or central locking).
It shouldn't be active all the time.
If the car is unlocked you should be able to do whatever you want, including removing the siren and disconnecting the car battery.
Yes, the siren is self contained. It has it's own battery! If the cars' battery is disconnected or the siren is disconnected WHILE THE CAR IS LOCKED, the siren will go off.
If you unlock the car but the siren still goes off, then there is some sort of fault.
So are you saying that, with the car unlocked, the volumetric sensors don't go off, opening a door doesn't set the alarm off, opening the bonnet doesn't set the alarm off, but disconnecting the battery does set the alarm off?
mitsub
(Donor 2023)
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Re: C5 X7 ALARM when battery disconnected

Unread post by mitsub »

Thanks for all the replies.
Since my first message, I've been thinking what I had done which was different to all the other times that I've removed the battery.
I wanted to change the radio, so with the key fob, I unlocked the car which had been locked the usual way (fob) since I left it the previous day, Opened the passenger door to release the bonnet catch. Lifted the bonnet and the alarm sounded, to say I panicked is an understatement I had never heard the alarm in the three years I've had the car and I've changed the radio a few times.
I'm not really sure what happened next, I think I put the battery lead back on and it stopped or I used the key fob. It happened with various combinations of which normally the alarm would not sound.
My routine now is, with an unlocked car I lower the drivers window, go to passenger side to release and lift the bonnet, then lock both front doors using the key only, and remove the battery lead.
The only difference I see is not using the key fob?
Hope this makes sense