For what it's worth, the accident experience in the UK suggests that
much more expensive accidents, including some injuries, have happened
as a result of gear warnings going off and causing the pilot to start
pulling levers, and losing pitch control, at low level, rather than
the relatively minor damage of landing with the undercarriage up.

Somebody else thought of, and I adopted, a much simpler and cheaper
arrangement than electric audible warning. I have a sticky label which
I put on the vario face. If it is still there when I come off tow and
start soaring, I have forgotten to raise the undercarriage. I then put
it on the air brake/spoiler lever.

If it is still on the air brake/spoiler lever when I come into land, I
have forgotten to lower the undercarriage.

So far, whenever I have remembered to use it, it has worked.

Chris N