"kony" wrote in message
...
On Mon, 22 Jan 2007 15:00:17 GMT, "John"
wrote:


For the sake of argument, let's say the unit is used very little and
the
receiver does not have a light.




Irrespective of usage, the receiver must be active all the time waiting
for
a call - like leaving a radio switched on - with the volume turned down -
it
will eat the batteries. Plug in ones are better.


I would suspect the receiver battery lasts at least as long
as the transmitter battery. Supposing one with a separate
transformer plug in supply costs $10 more, it may come close
to erasing any cost difference too over the life of the
unit, though the plug in type would reduce # of batteries
going into a landfill.

The transmitter is only consuming power for a few seconds at a time, when
somebody presses the button. The receiver is on 24/7, and it has to power
the bell/buzzer.