An occupancy sensor is hardware that detects whether a desk, room or zone is physically in use, typically via infrared, ultrasonic or camera-based counting. Sensors measure presence directly, where booking data measures intent.
The pragmatic view: booking plus check-in data answers most workplace questions at a fraction of the cost of sensor coverage, and sensors add precision where the stakes justify it, such as high-cost floors or lighting and HVAC automation. Many organisations start with the data they already generate and add sensors selectively.