Clattery when cold
Join Date: Feb 2012
Location: United Kingdom
County: Greater London
I had the same issue - random triggering of the tilt sensor. The sensor itself is part of the the ultrasonic volumetric board up by the mirror.
It's a white ceramic cube marked HL-P NS-25 that contains a liquid electrolyte, differential movement of which detects tilt. Unfortunately it is soldered to the board and an OEM-part only, that is now obsolete with no suitable replacement available, according to the very helpful Willow Electronics who specialise in this sort of component. They went back to the mfr and there was a one-off offer of 50 NOS NS-25 units at ~£60 each. Not having £3k spare I was unable to take advantage of this. Close inspection of the PCB showed my NS-25 to be leaking electrolyte slightly. I found a used replacement board in its housing, on eBay for £12, and that has so far been fine.
NB you can very easily swap the clip-in board and ultrasonic sensors between different housings, so buying a scruffy or wrong-coloured housing isn't a problem. Mine is black, most are beige or gray.
EDIT: You can just pull the plug at the board. That (obviously) disables the ultrasonic and tilt sensor, and you'll get a double-beep on arming but otherwise the rest of the alarm system is active and you don't get the false alarms.