how does a hotel not go bankrupt replacing thousands of batteries all the time?
A microcontroller in sleep state (or similar) draws extremely low power, micro or nano Amps. It only wakes up when it sees data on the card reader, reads the card reader data, and decides if it should open the lock. The motor that unlocks the door only runs for less than a second. Then the whole thing goes back into sleep state.
Hotel doors are only opened 10s of times per day, at most. A pair of couple Amp-hour batteries will last quite a while. Maybe replace them once a year. Tech with an electric screw driver maybe takes 1 minute per door, even a 600 room hotel only costs 2 days of labor once per year (max 1 week, if the tech is slow). That's not that expensive. And the tech's time is 10x the cost of the batteries, coin cells in bulk are dirt cheap.
A microcontroller in sleep state (or similar) draws extremely low power, micro or nano Amps. It only wakes up when it sees data on the card reader, reads the card reader data, and decides if it should open the lock. The motor that unlocks the door only runs for less than a second. Then the whole thing goes back into sleep state.
Hotel doors are only opened 10s of times per day, at most. A pair of couple Amp-hour batteries will last quite a while. Maybe replace them once a year. Tech with an electric screw driver maybe takes 1 minute per door, even a 600 room hotel only costs 2 days of labor once per year (max 1 week, if the tech is slow). That's not that expensive. And the tech's time is 10x the cost of the batteries, coin cells in bulk are dirt cheap.