2003 blob WRX with the cat 1 factory alarm upgrade...
car alarm started going off so I went out and unlocked it to stop, went to lock it again with the fib and the alarm is bleeping - the sound that normally indicates door not closed properly. After enduring all doors were closed I went and manually pressed all the door pin switches and bonnet switch to ensure none were sticking. Couldn’t see the one for boot lid. Still same problem persisting. Iv sat inside the car and no door open light on the dash is on, yet it will still beep. Is there anything else that can cause this? Low battery?

Had the same, it was the boot. Can’t for life of me remember the actual issue as it was sorted at same time as an MOT & wasn’t hugely important. Find the sensor/switch for boot and check all is good. Also a sticking boot mechanism will look like the boot is shut but won’t physically lock. This is not unheard of any car 👍🏼.

Just give an update on this - I used the sigma alarms last trigger isolation feature to narrow it down the bonnet switch which was the culprit - the switch physically seemed to be operational after I tested the continuity but was obviously the issue as the fault disappeared when disconnecting the switch. But a new switch so should hopefully be sorted once I fit that!