Local hero wrote:
My Brother-in-law has just bought a house where the previous owner had
died, so no-one to ask questions of. Inside there is a small (about 3x2
inches) yellow plastic box mounted on the wall, with a small black
plastic key (about 1.5 inches long) in it. To the left of the key hole,
still part of the box, is what looks like it might be an indicator of
some sort, but whatever position the key is turned to, the indicator
stays the same.

It is positioned by the front door, and there is another one in the
main bedroom.There are cables running to the boxes, but can't trace
them without a lot of removing of fixtures/boards etc.

There is a burglar alarm fitted, but he doesn't have the code and so
can't tell if it worked, or if it is related to this little key box.

It's probably a "panic alarm" box. There will be a large button to press
when you detect a burglar breaking in or already in. Pressing the button
will activate the alarm. The key is to reset it and would normally be
stored somewhere else.

--
Mike Barnes
Cheshire, England