Designers of public buildings have to be fairly careful about where they place power sockets. Aside from the question of public safety, anyone with a compatible plug can insert it and draw power until they get told to stop.
Today’s invention is a power socket incorporating a lock mechanism. This might have internal barrels (just like a Yale lock) which make spring-loaded contact with one of the three pins on the incoming plug. This pin will have a corresponding key shape formed on one side, so that only certain plugs can enter the socket and draw power.
Sockets could be designed to admit only a small number of different plugs (with each building or business having its own set cut by a conventional locksmith).
Foreign appliances would be excluded, preventing someone from using an electric fire in their hotel room or running a fast-food van’s fryer from a railway station supply. Picking the lock would be a perilous endeavour.
This approach might be extended to laptops, for example. Supplying each with a power lead with a key on the end entering the machine would decrease the chances of a machine being stolen when not attached to its (unique) lead. No-one would want to have to buy a replacement battery every time one discharged.