Derek ^ wrote:

What's an underload??

I think he meant under load. In other words the voltage when being used,
as opposed to the voltage produced when not connected to anything.

Have to say that we tried first a cheap wireless doorbell from B&Q in
my GF's place and it maybe worked half the time. Tried a more expensive
one and that worked maybe three quarters of the time, and then finally
the most expensive one they sell, which claimed a prodigious range that
would have supposedly worked about fifteen houses away. That worked
maybe 85 to 90% of the time. In the end we gave up and put in a wired
one with a mains fed bell for about five quid. Works 100% of the time.

Regards

Mark