The WeDo 2.0 motion sensor (part 45304) can detect objects up to about 15 cm away, depending on the shape of the object and its reflective properties. When an object moves, it changes its distance relative to another object (such as the sensor). Consequently, the sensor can detect motion as well as measure distance. It is sometimes called a distance sensor. Technical details: The motion sensor is an active infrared (IR) sensor. One of the sensor's “eyes” emits an infrared signal that bounces off an object and is detected by the other. The light is pulsed at 7 kHz. You might be able to see (and show) the flashing light using a camera phone. The sensor can work with 5 to 9 volts, with the WeDo set at 5 volts.