07 pt cruiser alarm

I working on a 07 pt cruiser (headgasket)
and after i had the engine torn down my girl
friend wanted to clean the inside. So i
hooked the battery up to let the windows
down and as soon as the windows got down
the alarm started going off. I had bought the
car not running but had tried starting it
several times and never had this pdoblem. I
dont have the original key fob just a grey
key and have herd that there is a alarm box
under the driver side of the dash but i cant
find it. I also tried unhooking the battery ,
that didnt work. It just kelp going off as
soon as i hooked it back up. I dont know
what else to do. Dont have money to send it
to a dealer sence im already doing the
headgasket.