What does your car's seat occupancy sensor system do?

A vehicle’s passenger occupancy sensor detects whether a passenger is in the seat and decides whether or not to allow the airbag to deploy in the event of an accident. If the sensor determines a weight on the seat is not a person, the airbag does not deploy.

The traditional seat occupancy sensor is a mat sewn under the upholstery on the surface of the seat. Beginning in 2006, manufacturers began replacing traditional seat occupancy sensors with occupancy classification sensors that not only determine whether the weight in the passenger seat is a person or not, but also attempt to classify the size of the passenger and decide whether to release the airbag at a slow, medium or fast speed to avoid injury.