The Yam remote control switches seem to be very common on eBay and are surprisingly cheap for what you get. The insides seem relatively acceptable give or take a bit of poor track clearance between mains connections.
The circuitry is pretty much text-book for the application with a small microcontroller doing the decoding and relay control while a discrete RF receiver module based on an LM358 converts the received signal to a level the processor can deal with.
Here’s a general eBay search link for this type of unit, but note that most are intended for 220-240V use.
The circuitry looks like it could be hacked to power it from an external 12V DC supply quite easily as long as it is not an electrically noisy supply.
The unit is only really intended for low current loads like light fittings, but again is open to technical modification with things like external solid state relays. (Treat low voltage side as being live at full mains voltage.)
I’m not sure if there is different coding between units. So I’ve just ordered a couple more to find out…..
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