Think probably easiest to explain what I need it for and the kind of solution I envisaged, and if there's a better way to do it I'll be interested in that too.
I'm part of a tennis club, we have introduced new rules to minimise the spread of covid. You have to book to play in advance. We charge a yearly membership, and don't want to move to a pay-per-booking model (we have very few costs, thousands of pounds in the bank and some low-income members who would probably be upset about it and stop playing).
The problem is that people book to play but then don't turn up. We've restricted bookings to one or two a week by a member but it keeps happening. The bookings are anonymous except to the Skedda administrator, who obviously can't hang around the courts all day and write down whoever didn't turn up.
There is no WiFi on site (though there is power), but I thought of a possible solution, and wondered if it has ever been implemented. On the court, a screen which displays an arbitrary sequence of numbers, which changes every hour, taken from a simple text file which lists the time and date next to said number. This number could be represented by a qr code.
On the user side, the user has a smartphone app which scans the qr code, and checks the number against the date and time on the server, and records that the booking was actually used.
Does this absurdly specific thing exist?