hahaha im sorry i have to laugh because i remember i was in my hs parking lot and it did the same thing i didn't kno what was goin on. i was like whoa i got an alarm cool
but it did it completely randomly i dunno about yours i have a 1991 and and i figured out if you unlock it from the inside (windows rolled down) and open it with outside it goes off. The fact that it won't let you start the car i think its a saftey device in case anybody breaks into your car they can't start it however when it happened to me i would just let it sit for about 5 mins not doing anything (messing with the locks won't do anything after 5mins) it should start. did you recently install a new battery cuz that makes the alarm go haywire too?