British plugs with built-in surge arrestors. (With schematic.)

I got these just to find out how they had implemented the surge protection in such a small space. It's an odd but also clever design that is based on existing electrical parts.

I'd guess that these would be useful in a situation where there was a risk people might unplug a typical surge protection adapter. If it's on a flex then it's less likely to get removed. But it's also less likely to get changed if it fails over time.

These units came from CPC (part of element 14) in the UK. I'd guess similar devices exist for other styles of plugs too.

If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
http://www.bigclive.com/coffee.htm
This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.