Alarm keeps going off randomly

[Terryvision]

99% of the time its the bonnet switch, it can be unplugged without any issue... unplug it set the alarm see if it goes off

If no alarms.... it's your switch

 

[benlumley]

Hi all, I have recently purchased an 03 plate 3.0l z4 and am having problems with the alarm going off at random times. It is quite frequent and there appears to be no cause. I have read it may be the bonnet sensor and have tried locking the car with the key to avoid turning the alarm on but it still does it. Any ideas what might be causing it? When the alarm does sound it's just the beeping, the lights don't flash and there are no visual signs that anything is happening. I've had to leave my car unlocked for now so I would like to fix it quickly.
Many thanks for your replies,
Aaron

When my alarm plays up from time to time - I lock the car the old fashioned way, key in door, which seems not to set the alarm at all as far as I can tell.

 

[Charlesell]

I'm having an alarm problem at the moment too. I have been locking the car on the key for days as it's the only time the alarm doesn't go off. But immobiliser still works.

2.2i SE (ish lol) Roadster. K@N cold air induction, Powerflow twin freeflow exhaust, 18" 255 Deep dish alloys, race clutch,gearbox, tuning and several remaps
And Red Grills
But me alarms a bitch lol

 

[kevver]

Hi All.
I developed this problem in the last month and as it's not good policy to leave a car unlocked, I thought I would do some research.
Reading this forum and other forums, it seems quite common that the fault usually lies with the bonnet sensor. This can be found at the back of the bonnet between the two diagonal torsion bars. It's similar to the press buttons you would find in old car doors by the hinges.
This is how I fixed my problem:
1. Take out plug on bonnet sensor. Shut bonnet and lock car. If alarm goes off the bonnet sensor is not your problem. If alarm is silent as it should be, the sensor is the problem.
2. Lubricate sensor, plug in and tape down sensor fully. Leave bonnet up and lock car. If alarm goes off, you need to replace sensor (about £25, me thinks). If alarm does not go off, it means that the bonnet is not pressing down hard enough on the sensor to make it work properly. I found that by bending the switch mounting bracket very slightly up towards the bonnet, it solved the problem Don't buy a switch until you've tried this first.

 

[baz of eb]

Big time thread resurrection. Just tried this tip today and has solved my issue. Big thanks if you are still around this forum.

 

[paddy wright]

Sounds like a bad battery to me.