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I can't speak for Glyn & Trystan, but there are several practical difficulties that need to be surmounted. The first one is the power supply. WiFi typically needs much more power than the low power devices that we typically use, and that could be difficult to arrange inside a small unit. The second, and much more serious problem, is safety. The physical space available precludes the use of isolating transformers, therefore a galvanic connection to the mains supply is unavoidable. This means that 'live-line' working practices for testing and configuration would be necessary, ignorance or even a moment of forgetfulness could well result in a fatal accident. So the only realistic solution that I can envisage would be to market a professionally manufactured, certified and sealed unit.

Thanks Robert, nice reply regarding wifi! I actually regretted using that in the title as I am not especially interested in wifi communication, just a way of monitoring individual sockets.

Your second point is a good one about risks of developing this sort of tool. As I said, I am new to this, so I have no idea what has been developed! I was just wondering whether this sort of application is on the horizon, or too far off to consider...

Would a small unit that could go on the switch when inserting the wires into the socket be sufficient perhaps? Just an idea...

"Would a small unit that could go on the switch when inserting the wires into the socket be sufficient perhaps?"

You're obviously thinking in terms of the common plug-in energy monitors that are readily available in the DIY sheds and elsewhere (like this one, only selected because it was the first to pop up in a search!). The immediate question is how many versions would be needed world-wide, and at what price could it be made in order to be viable?

Individual appliance monitoring is something that's often requested, that can often (usually) be done by monitoring individual circuits leaving the distribution board. It's mainly in the UK where the ring final sub-circuit is common that this cannot be done, and a unit such as the one you envisage is necessary.

As I wrote earlier, I can't second-guess what Glyn and Trystan's thoughts are.

Interesting.  I didn't know about rings.  Is this a fair depiction:  https://en.wikipedia.org/wiki/Ring_circuit#/media/File:Ring_circuit.svg?

For per-circuit monitoring, could you wrap a CT around both of those brown wires coming out of what I assume is the breaker?  Or if you were feeling really extravagant, wrap a CT around each of them, and treat them as two different circuits?  That might be useful for generating an alarm to let you know the ring has been broken.  Presumably when all is well the currents seen by the two CTs are fairly similar, whereas a break in the ring would show up as a big delta?

I did initallially mean a plug-in version in the first post, but my main interest would be in a monitoring device that could be inserted in the socket itself. Or a socket that could be purchased with the functionality already installed. What I meant by switch, was slightly incorrect as I was just thinking of a light switch, and just meant something that could be wired into the cable manually. The wikipedia image is helpful, as I was thinking of adding a device to the cable coming off an equivalent of the junction box shown, although you could have that branch all within the socket back box itself. If well designed it could also help with the fiddly job of screwing in the wires - often quite hard!

I can't see any built-in monitoring devices, which was why I was asking whether it had been discussed here. However, I haven't looked that hard!