It was a box attached to a rental tv. You rented the tv and paid for it with coins. It had electrical wires coming out of it to the tv. Tradie Brother told me that there wasn't a direct relationship between the money you put in to watch tv and how much the tv rental cost, so therefore, when the box was emptied, you received some money back, an incentive of some sort I think.
When I told R this, he remembers them in England, along with the coin in the slot gas meters.