Featuring an advanced solar cell power supply and calibrated temperature sensor, the EnOcean STM 330 ISM-band transmitter module derives its power from either the on-board solar cell, an external energy harvester or an external 3V battery. To bridge any gap if the energy harvester experiences energy drop off, an energy storage element kicks in to ensure continuous power supply. The module also features a configurable cyclic wake up. A radio telegram is sent after wake up in case of a significant change in temperature or set point values – or if a room occupancy button is pressed. When no input change is recorded, a redundant retransmission signal is sent after a configurable number of wake-ups to declare all current values.