Paul__B:
Look, just keep it simple.If you are going to use a controller to control appliances, then the controller does it all.
I get the impression from his post that he wants to use a two way switching system with one of the switches controlled by an Arduino. He needs a double throw relay and a double throw (two way) switch for that. There is then no need to detect what state the relay is in. Throwing the two way switch will invert the state of the relay.