A long time ago I built a "touch switch" that essentially worked
because a human body is a reasonably good antenna for the 60Hz Hum
that's all around us these days.  Touch an otherwise unterminated
pin of a generic op-amp configured for "infinite" gain, and I got
a nice 60Hz waveform at the output suitable for driving a flipflop
and relay...

Since then, op amps have only gotten better.   Is it possible to
build a circuit NOW that reliably detects 60Hz hum with only a
small internal antenna?  How close to power wiring would it have
to be?  In particular, can I make reliable lithium power-fail
safety lights that I can just stick to a wall anywhere in the
average USian home?

BillW
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