I considered the double throw relay as a possible solution to knowing the state of a latching relay until I saw the cost. When you spend as much on a relay as the rest of the circuitry, it gets a little silly. That's why I've been researching how to sense that current is flowing in combination with voltage being available.What I want to do is power the electronics of a switch with the power that's available in the switch box (no batteries or separate power supply) This means that I have to have a tiny power supply that takes mains voltage (110 for me) and gives me 5V to run the circuitry. On a multi-switch setup, where there are both SPDT and DPDT switches in the chain, finding power and knowing the state of the latching relay can become quite a task without rewiring the switches.
@TorremolinosThanks for the reply. I did go through your project, but couldn't really find anything related to controlling and monitoring the current status of the light in existing 2-way switch circuits. Please provide me a link or additional info, if I did miss on something.