An automatic hand dryer uses a small infra-red sensor in the drying area. When the sensor detects a solid object that is warmer than the surrounding air move into the area, it turns on the fan and the air starts to blow. The sensor responds almost instantly to the presence of an object and will also switch off the fan once the user’s hands are removed.

This means that there is no need for a switch, and the dryer only operates for as long as is necessary. Older designs which used a button also featured some functionality that appeared automated, in that they would run for a pre-set duration when activated, however this could not adapt, which meant that the dryer would continue to work even if the user had moved on without completely drying their hands.