The slam switch goes over a second link. I have long range wireless modems that drop a TTL output within 100 mS of loss of the master node carrier or under a DOS/JAM situation. Since these do not use your classic WIFI protocol, they come as close to possible of being a "virtual" wire. If I turn off power to the master transmitter, less then 100 mS later, no interlock relay.
Still vulnerable to interference, which is why most people (95%) should use a wire.
Steve
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...