I Know the feeling -- I had the same problem with the factory alarm on my 2000 TL -- I didn't know what was setting it off. - However if I left the Hood open (not up - just unlocked) it was fine --Didn't go off at all???

I took it to an alarm specialist to get an after market one put in - I explained the problem - and he was going to disable the hood pin switch sensor for the alarm - in order to put in the new one.....

... Then he said that the sensor was so dirty he couldn't find it (I guess after all the grease and Rust proofing I have to do in Toronto it was just build up).
He emptied a can of WD40 and scarped of what he could - and just like that - the Factory Alarm works fine!!!! -I've had no problems since, (knock on wood) and that was 2 1/2 months ago. The best part is he only charged me $20!! - What a deal, The was the most I ever paid for WD40 but well worth it!! Now I can lever my car in peace.

What you are looking for... if this is the same problem, is a little blue square on the inside of the hood latch... spray it with the wd40 (non greasy) and clean it... then see what happens. (with your fingers crossed).

I hope this helps you, if not you, someone else who has had this problem, I know I've searched all over the net for a solution to the "Ghost in my Alarm" with no Luck - I guess you got nothing to loose by trying this option- And your neighbours will be happy.

Cheers,
Lex - In Toronto.
www.lexcorpmedia.com