nospam writes:

DaveC wrote:

On Fri, 7 Jan 2005 17:09:10 -0800, Palindr➸»me wrote
(in article ):

Or you could glue a bit of aluminium foil to the rocker of the switch
and position an LED (for greater range, use a laser diode) and
photodiode so that they "see" a reflection of each other with the switch
in one position but not in the other. With the added advantage that you
can make the alarm go off even before the switch is altered - the
approaching finger getting in the way would do it...You could put a sign
on it ..."do not even think of operating this switch"...

It's a float-operated microswitch in a well.

Then it should have NO and NC contacts and you can wire up your relay and
battery to the contact pair which never have mains across them.

I bet it's down in the well and totally inaccessible.

There have been a few valid suggestions.

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