Followup:

The neighbor's problem was solved by replacing the front door unit with a
wireless unit from Carlon/TruValue for $20 that alleges to transmit to 150
feet. Model # upon request. The $10 unit alleges 75' so I splurged and
bought her the $20 one, which also plays Dixie, the Star Spangled Banner and
some other tunes that are easily (maybe too easily) changed from the
doorbell button. It worked well enough that I'll be getting one for us, too
because our side door unit failed and we just never bothered to replace it.

The range is yet to be thoroughly tested, but it works from the side of the
door where the old one didn't. The method to vary the frequency is very
odd - five exposed through the case metal links you can clip with very small
wire cutters or nail clippers. One way changes only for many people.

The old unit now serves as the side and basement door bell. The new unit
also uses much cheaper batteries - 4 AA's and two button cells instead of 3
D's and a 12V alkaline "stack" battery. The tradeoff is that the new unit
sounds tinnier and isn't as loud. It comes with a beltclip and that made me
think I might get two of them - mount one inside and clip one to my belt for
when I am working in the backyard where I sometimes can't hear the doorbell.

--
Bobby G.