harryagain presented the following explanation :
The other good news is that they use electricity all the time.
Whereas a battery operated doorbell only uses power when a finger is on the
button.

If you meant the wireless type, the bell unit uses a constant amount of
current to keep its receiver working. The bell push only uses the
battery when the button is pressed and it transmits.

An old and chattering transformer will use more current than one in
good condition.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk