To me that looks like it is the whole alarm, one of the very cheap things they would sell in the late 90s early 2000 in places like halfords and Argos. Is there any specific reason you need to know what it is, other wise just bin it and fit something more modern
Jeez going back to alarms from the old days, some right bodgery was used then, splicing into wires and just taping wires together I paid a pro to fit one for me as it was cool to blip the fob and see the indicators flashing. Eventually I had to rip it out as the car would cut out or alarm when driving. I've learned lots since then and to be honest prefer to work on my own cars.