On Tuesday, 13 October 2020 22:19:23 UTC+1, ARW wrote:
I believe it was AICO CO detectors that failed the Which tests (on a
sample of 3)

That was the 208 at £21.

I got the EI261ENRC which was a bit more expensive.

Although it's discontinued now and its replacement isn't hardwire interlinkable.

Anyway, the presence of a box on the wall keeps surveyors happy. I don't expect any will have a CO tester along with the damp meter.

Owain