snip

I got one (gift for good behaviour!) some 6 years ago, it's made by
Science Museum and cost about £45 at the time, it still works perfectly
to this day and I have probably only replaced the batteries twice.
Unfortunately it is no longer available. My Dad got one a year ago from
Amazon, made by a German company called Hama. It seems to work
reasonably well but the stand for the inside unit broke after it fell
once. Both units very similar readings (±0.5ºc) and also the Vaillant
outdoor sensor gives the same readings we have so I'm guessing there are
both relatively accurate.

--
David