A distance sensor detects whether and object is in front of it and provides some indication of how far away it is. Distance sensors could also be considered a more advanced form of a proximity sensor.
Distance sensors can be used to detect many things in the smart home from movement of people to the depth of water in a tank. The two main techniques for range/distance sensing are using ultrasonic sound or infra-red light.
We are using the JSN-SR04T waterproof distance sensor to detect occupancy in our shower. Because it measures the distance from the ceiling to the top of the person in the shower, we can even measure how tall the person is and guess at who they might be.
We are now also using the Sharp 2Y0A21 infra-red distance sensor for similar applications.
