I'm not sure about the model number. The cover itself simply pulls off.
Underneath the cover is the circular case of the unit, but no holes. There
appears to be a small square hole on the side of the unit. (side meaning
side of the cylindrical base, but not inside the circle itself). I could
try pushing a small screwdriver sideways (parallel to the ceiling). Is this
the hole you are talking about?
<<Call the alarm company first if it's monitored!
Assuming it's a model 449 .. There is a small vertical slit on the
side of the unit. Push a trim screwdriver in the slit and the cover
will hinge downwards. This will give you access to the mounting
It's easier to separate the terminal block from the unit, then to
unhook the wiring. (you'll see what I mean)>>