I've used a system that each worker of the building would be given a card. In the hall, there's a card reader. There's multiple elevators in the same building.

I've used a system that each worker of the building would be given a card. In the hall, there's a card reader. There's multiple elevators in the same building. To use the elevator, one would need to tap the card against the card scanner. Then the screen on the scanner would tell you which elevator's gonna serve you.