On 11/8/2015 5:51 AM, Retired wrote:
Maybe the enclosure from a small stereo speaker ?

I think that would tend to be large -- even for a "small" speaker.

The advantage/appeal of a smoke detector "case"/cover is that they
seem to be designed to be as unobtrusive as possible -- folks
don't really want to *notice* the smoke detectors in their homes, etc.

Along that same line of reasoning, I've seen some *indoor* PIr detectors
for alarm systems that "try to be unobtrusive" (same rationale: folks
don't want to *see* the stuff that comprises their alarm system) that
might be usable in wall-mount scenarios.