I did some research after staying in a Vegas MGM property and the minibars [1] seem to use IR beams to detect if a product has been removed. They also can be hardwired via Ethernet or use wireless protocols like zigbee. It seemed that in my room it was wireless as the thermostat model supported zigbee. I also saw that the fridge could be locked remotely (!) on some models. [1] https://bartech.com/