alarm goes off radomly help!

[fairlady_z34]

so came in to work this morning, went in for about an hour then my car alarms goes off. no one was parked near or around my car at all. i went outside to try to just it off it wouldnt shut off, and was like wtf. i then turned the car on, alarms goes away this time when i shut it back off alarm comes back on but very faint and sounds like alarm has been going on for hours and is running out of battery but it isnt(car starts perfectly fine). im thinking its a bad sensor, or maybe moisture due to the rain today, what do you guys think? also alarm wont shut off when i try to shut it off so i just pulled the battery out so it wont drain my battery when i try to go home. sounds kinda like the alarm wants to go off but it doesnt.... any ideas?