The SHT-12 C4 handheld transmitter allows remote control of up to 4 functions of a radio module or receiver from the SH-12 radio series. A blue LED indicates the transmission operation. It not only represents transmitted radio signals but also provides information about the quality of the radio communication and the transmitter's supply voltage. The red LED shows either the status of the receiver's supply voltage or the receipt of the receiver's confirmation, depending on the wiring at the radio receiver. An integrated buzzer also acoustically signals the confirmation from the receiver. If confirmation is disabled, every change in the button state is reported instead. The handheld transmitters of the SH-12 radio series operate with extremely low interference due to their special transmission characteristics. With interference-resistant radio transmission and extremely short response times, ranges of over 1000 m can be achieved. For strong narrowband interference or the use of multiple parallel radio systems, the operating frequency can be adjusted to individual needs. The SH-12 radio series can be operated in both unidirectional and bidirectional modes. In bidirectional communication, the transmitter automatically adjusts its transmission behavior based on the quality of the radio link. The transmitters are factory programmed with a continuous serial number, ensuring greater security and making each transmitter a distinctly identifiable unique piece.