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> the switch on the wall only has the positive terminal in, the ground is wired directly into the bulb socket.

This is the standard practice in many countries. Wiring the return wire is unnecessary.

> So smart switches just don't work.

This is false.

There are remote controlled switches that are designed to work with a single wire. I have one right now in my room, they utilize an energy-harvesting circuit to obtain energy from the changing magnetic field surrounding the AC line to charge a capacitor to power itself. Also, it uses 433 MHz RF, so it means it doesn't have Linux and IoT craps embedded inside, no firmware upgrade, no factory reset.

Yet, I can capture the control sequence using RTL-SDR, and use a 1$ RF transmitter from my Raspberry Pi to control my light programmatically if I want, though I never needed to, fortunately.

[gambiting]

Interesting, but I suppose I got something wrong then, as there must be a reason why pretty much no company offers smart switches in the UK market even when they have smart switches in other markets.

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> no company offers smart switches in the UK market even when they have smart switches in other markets.

Honestly I don't know, I'm not sure about the UK.

Perhaps those "smart" switches can't be powered by this technique due to their higher power consumption? But then, why can't one just use dumb RF switches, and put the heavy-duty digital "brain" inside a separate unit as I suggested? Because the encoding scheme doesn't scale? But it should...

In all possible ways, the same principle should be fully applicable in the UK... Sorry, I don't understand, it should be answered by someone who knows better than me...