Hi. I'm replacing an old external sounder with a new Texecom Odyssey 4, which allegedly has wall tamper. Inside, there are just two contact switches. One switch is closed by tightening the screw that retains the sounder box lid. The other switch is closed as the box lid is positioned and pushed down onto the back plate - this switch does not swing out of the back of the back-plate (i.e. to be squeezed by a combination of the wall and the box lid). Where is the wall tamper - am I missing something obvious?

One of your wall screws will pass through a piece of plastic that will break off when the backplate is removed from the wall , thus operating the tamper.

As fastcar-there will be some writing saying 'Do not over tighten screw' and two ridges that should stay in line, as you could fracture the tamper switch plate yourself.