ya, most likely an alarm....

if you wanna trace it without taking your car apart try this and see if there is any results of siren chirps....

turn ignition on then immediately off, within 10 seconds, hold the button for 3-5 seconds... if there is a chirp then there is an aftermarket alarm...(even if there isnt a chirp there still could be aftermarket, but this will tell you if everything is hooked up)

however, if you do this, then you have entered programming mode, so dont push the button anymore or you may cause some problems....just dont touch it and it should chirp again, and so exiting programming mode..

just a quick way for you to check...
granted, dont rely on if it doesnt chirp it not having an alarm, it could be disconnected or missing parts....definately look at it deeper to see if its just remnants of an alarm...