Magic sensor on a finger. It is powered solely by the changes in temperature or pressure it measures, requiring no battery. This long-lived autonomous sensor is only active when there is a change to measure. Voltage is generated in pyroelectric materials by changes in temperature, or in piezoelectric materials by changes in pressure. The voltage is converted into a radio signal transmitted by an antenna. This data can be picked up by a receiver up to 20 metres away. The sensor can be used to measure tyre pressure or the temperature of cooking food. It was developed by Siemens, Munich-Perlach, Germany.