Andrew wrote:
I would very tempted to switch to Octopus(sy) just to be able
to borrow one of these things, but then I would a smart phone
too. Damn.

I've got one. It's really handy for detecting cold spots - for example:

Uninsulated roof ceilings
Cavity walls the installers forgot to insulate
Leaky loft hatches
Edges the loft insulation doesn't quite reach
Solar gain

No smartphone needed if you fancy some DIY:
https://hackaday.com/tag/flir-lepton/

Theo
(which reminds me, I should take a look at the radiator pipes with it...)