I already have a few North American locale kWh meters I attach to things (more reliable than a kill-a-watt for long-term logging) for fun but I wanted to see if I could get hold of a pre-pay meter.
I guess back in the day in some regions the electric company would supply a master meter for one building or a group of buildings and if the landlord wanted to rent out the spaces wired to the master meter separately but either the rental times were very short or they didn't trust the tenants to pay the bill they could install these in each location. You set the cost per kilowatt unit and then you just fed money into the meter to keep the lights on. Later versions used stripe cards then it was chip/RFID cards that could be topped up. They are also apparently not well loved because often the landlord would bill at a rate notably higher than what the utility company was billing the landlord.
Interestingly it seems they were/are only really popular in the UK. They seem to be increasing in popularity in southeast Asia but in countries like Australia or the United States they are not are were not really popular or their assets were controlled to the point they could not be found surplus. As such I had to order two Smiths meters from the UK for $50 each and they should arrive next month. They will work as long as you run them on 220/240v service but being wound for 50hz they will run faster than they should. Were 120/240v 60hz meters just not that common postwar?