Please help!! Sigma M30 alarm keeps going off when arming

[Trig]

Hey everyone,

After changing the spark plugs on my 2001 WRX (UK GDA), I went to lock the car and noticed the soft alarm started going off — similar to the chirping sound you get when a door is left open. However, this time it doesn’t stop — it just keeps chirping continuously.

 

I initially thought it might be the bonnet switch, but before, if a door or the bonnet was open, it would only chirp a couple of times as a warning — not endlessly like this.

 

Anyone experienced this before? Wondering if I’ve accidentally disturbed something while working under the bonnet, or if it’s just a coincidence.

 

Any help would be appreciated!

[Mr B]

double check bonnet switch not bent out of position or wiring an issue .
What did you work on ?
was Battery disconnected for any period of time .
Not unusual for issues with m30 alarms at this age, siren backup Battery goes bad and can also leak and corrode board causing odd problems, relays in main unit can go bad too .
If Siren issue you can leave siren unplugged and use fob/vehicle like normal .

I done some MOT welding work on a Outback last year and had Battery disconnect while welding and that drained a failing Battery in the Siren .
When reconnected battery we had the low dB warning bleeps and after few minuyes alarm would go off randomly. had strip siren and found bad leaking battery that shorting/damaging control board.
A decent used siren and a new rechargable battery resolved that one but that was almost couple hours work find fault and chase parts.
The fun of electronics lol, hybrids and electric cars be fun if manage reach age of this ...

 

[Trig]

2 minutes ago, Mr B said:

double check bonnet switch not bent out of position or wiring an issue .
What did you work on ?
was battery disconnected for any period of time .
Not unusual for issues with m30 alarms at this age, siren backup battery goes bad and can also leak and corrode board causing odd problems, relays in main unit can go bad too .
If Siren issue you can leave siren unplugged and use fob/vehicle like normal .
 

I only worked on spark plugs and disconnected the Battery to do them. Battery is secure and free of corrosion. I’ll see if I can just disconnect the horn for now but would like to solve the problem. I was going to check the bonnet switch but doesn’t that usually only beep a couple seconds then go away when a door is open? I’ll give it a check though just in case. 

[Mr B]

Yes usually just beeps few times but these old electronics don't always respond how they should .
Assume it likely bigger fault but best assuming nothing and inspecting/testing everything starting with basics .

[Mr B]

M30 manual if needed >
 

m30.pdf

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5 minutes ago, Mr B said:

Yes usually just beeps few times but these old electronics don't always respond how they should .
Assume it likely bigger fault but best assuming nothing and inspecting/testing everything starting with basics .

I was thinking I could have knocked a ground wire somewhere but couldn’t imagine where. Since it keeps going I’m assuming it’s not the bonnet switch

[Trig]

4 minutes ago, Mr B said:

M30 manual if needed >
 

m30.pdf 118.43 kB · 1 download

This could help. Thank you!

[Mr B]

I wouldn't worry too much as it pretty easy and cheap to source used working M30 alarms and swap over faulty modules if that turns out be the case .
The alarm siren can be dismantled by hidden recessed screws so Battery can be replaced and board can be visually inspected .
Main control unit pretty easy swap (just be sure comes with a working fob or 4 pin code so can program your fobs easily) .
I have changed a few main control modules and sirens over the last 10 years .
You could also remove/bypass or replace with new alarm, lot of owners on more basic old models such as forester and outback don't really want go new alarm route for cost and lowest cost bypass means remote locking lost .