In article ,
GregS wrote:
Battery operated thermostats don't have a conventional relay - ie one
which takes power all the time it's made. That would run down the
battery in short order. They use some form of 'motorised' switch, which
only takes power when it changes state. On mine you can hear it operate.


I always assumed a relay, and yes they are loud. On a soild state unit I
could also hear a click, but I think that was from current flow. If
units use a switch, I hope they have a safety overheat breaker.

Certainly in the UK it's a form of mechanical switch. It can carry mains
or low voltage AC or DC - not really possible with a solid state device.
My guess is it may be piezo operated. But that's only a guess. Mine is
rather louder than a relay.

--
*Just remember...if the world didn't suck, we'd all fall off*

Dave Plowman London SW
To e-mail, change noise into sound.