1984 928 alarm

I am having the usual problem of alarm going off sort of randomly. What I so far know is that the alarm is not original equipment and that when it sounds it appears to come from the firewall area. I have solar narrowed it to the pictured gizmo:





Any ideas as to whether this an aftermarket alarm?

I should add the unit shown is just above the passenger side (right of car) and the image below is taken from the front/driver side: