Wireless sensors are wireless sensors equipped with a radio modem. For wireless sensors, which usually operate with their own power supply, power consumption in sleep mode is an important parameter that has a direct impact on battery life. With appropriate energy saving techniques, wireless sensors with ZigBee can operate for several years on one battery.
In addition to the battery-powered wireless sensors, there are also the battery-less ones. These sensors transmit their data with battery-less wireless technology. They obtain their energy with micro- energy harvesting from the ambient conditions, from light, temperature, air movement or pressure.
The license-free ISM bands between 315 MHz and 434 MHz, 868 MHz and 870 MHz( SRD), 902 MHz and 926 MHz, and 2.400 GHz and 2.4835 GHz are available for transmission. The frequency bands up to 434 MHz and between 868 MHz and 870 MHz are mainly used in Europe and are suitable for medium transmission distances in buildings. The 2.4 GHz band can be used with low power over short distances of a few meters.