Hi Dave,

One method might be to generate a small AC signal on an ISM frequency such as 13.56 Mhz and couple it through a small transformer to the two switch contacts. An HV capacitor can be used to prevent mains current through the transformer. Then monitor the current into that transformer. If the switch is closed there will be full current no matter what the power grid status. When it is open, the current will be a lot less. This can be pulsed if battery operated, to conserve battery power.

A small choke on one side of the switch prevents load or line conditions from shorting out your RF signal while the switch is open. Or course, you have to abide by EMC rules and obey electrical safety rules (isolation etc.). IOW, you really have to know what you are doing and be very familiar with safety and other legal regulations before doing any of this.

Also, make sure the pulses from the switch action don't fry anything.

Regards, Joerg

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