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[unlucky alf]

the last couple of days [including 10 mins ago] my alarm has gone off, its not the sounder side [if it has it] but the standard horn side, the interior sensors are turned off via the dash button so it shouldnt be them, after the horn has stopped waking up the neighbours the hazzards continue to flash, does the alarm have a knock sensor fitted or is it only on the doors, anyhow any ideas as this is upsetting the neighbours,,,,cheers

[markey mark]

bonnet sensor tim ! mine was same few weeks ago ! dissconectted it to make sure then replaced with a spare  

[Ian_D]

dont think they have knock sensors, but I'm just guessing at that.

Try unplugging the bonnet switch as they cause problems like this (its on the right hand side of the engine bay somewhere - next to the n/s top suspension mount.)

EDIT: To slow - thats what happens when you have msn messenger installed  

[unlucky alf]

cheers chaps, if i disconnect it can i assume that the rest is still going to work o,k or are they wired in series,,cheers

[Albatross]

Mine did this on and off for about a month about 6 months ago and then never since.

Weird. I reckon there must have been a mouse inside the car setting it off or something.

[unlucky alf]

well lets hope that shuts it up! it always seem to go off in the early hours when im all tucked up in bed as is the "law of sod"] is there any point in replacing this switch as the doors have to be opened anyway to open the bonnet

[Andy B]

well lets hope that shuts it up! it always seem to go off in the early hours when im all tucked up in bed as is the "law of sod"] is there any point in replacing this switch as the doors have to be opened anyway to open the bonnet

As said, it's not usually the switch itself but the bracket it's fixed to. It's a normally closed switch, that's opened as the bonnet closes but then closes when the bonnet's opened or flexes due to heat  :-? If the switch is not there it can't close, so the alarm is happy. Providing the switch is OK it'll just be the bracket.

[feeutfo]

As Andy says, on my pre face lift, i just bent the bracket up to meat the bonnet so it gave more contact when closed, thus pushing the switch further down. I always put it down to the weather/heat/ rain making the bonnet expand and contract?
That just being enough to set it off with bracket being a bit low.

 On my face lift they moved the bonnet switch to the drivers side wheel arch, a much more solid mounting point, which confirmed my theory, imho.
So yeah, basically, just bend it up a bit.

[Andy B]

......
 On my face lift they moved the bonnet switch to the drivers side wheel arch, a much more solid mounting point, which confirmed my theory, imho.
So yeah, basically, just bend it up a bit.

But, as MarksDTM pointed out to me, you also have an bonnet switch loom plug over on the passenger side too.  :-?      

[unlucky alf]

thanks chaps ive disconnected it for now & will leave it for a few days to make sure it is the switch, will test the switch in the meantime with a meter to see at what point it closes, but going on what others have said i`ll probably give it a tweak even though i still cant see the point in it in the first place

[davlad22]

dont think they have knock sensors, but I'm just guessing at that.

I would be inclined to think otherwise, we've had astras and even on the omega when it rains or hails REALLY hard it sets the alarms off.  

[Dave DND]

dont think they have knock sensors, but I'm just guessing at that.

I would be inclined to think otherwise, we've had astras and even on the omega when it rains or hails REALLY hard it sets the alarms off.  

Some of the early interior sensors were also Frequency sensitive to allow for broken glass, and these were often set up by the dealers by rattling a set of keys inside the car to get the correct sensitivy for them.

Problem was that hard rain and hail on the glass can often hit the same frequencies as the glass actually breaking !! - turn the sensitivity down a little and all should be well.

 

[unlucky alf]

right the update is; i disconnected the bonnet switch & while i was at it turned off the interior sensors via the dash button, today the bleedin` alarm went off again!, so i suppose the next thing is to remove the door switches & check them, cant recall seeing a switch for the tailgate though, has this got a mercury switch? if there is anything else to check please let me know as im on an RAF base all weekend & they take a dim view of alarms going off!!

[unlucky alf]

cleaned up all the door switches today, went to the shops & parked up, 3 mins later my alarm was going off again!, so now its going to be wire checking time where abouts is the alarm unit as im figuring thats the place to start first.

[Dave DND]

Long shot - but how about a faulty / discharged back up battery in the siren giving a voltage drop problem?

Clutching at straws I know ?