hi there, i have a 1998 volvo v40 1.9se - last night at 4.am the alarm went off for no reason, i reset it and it went off again, so i left the car unlocked and it locked itself few mins later and again alarm went off, so i used the key to lock the car and all was well. is there any kind of problems or faults that can occur with the alaram system? thanks. martin

 

The door lock will go bad and cause the problem you have.

 

I found it was the sensor under bonnet..I just lock with key now no hassle

 

alarm backup battery on siren may at it's end of life.. s40 I don't think u can read out alarm cause. P1 and P2 chassis is the one that I know u can read out alarm cause. hope that helps