alarm problem? on 996

[kagey]

when i lock my 996 it sounds the horn and the interior light comes on and then goes out. ive checked the handbook and it says poss causes are open glovebox,door,bonnet,boot. these are all off and/or closed. any ideas before i put it into the opc?

[silver993tt]

Is there a small compartment behind the handbrake (had one on my Boxster S)? That used to be slightly open regularly and took me some time to find it. It gave the same symptoms.