The F21-2S/D is a mini transmitter which has 2~6 commands. It is a low-priced device used for electronic chai hoist/monorail. It consumes low power as its plugged in 2AA batteries can last up to 4 months. Its DC models are specifially designed for mobile devices as they have additional shock resistant relay. Users can have more than 4.3 billions of unique ID codes for this device. It works on temperature range from -35°C~+85°C. It is enclosed in a gIP65-protected material and can work on Microsoft Windows.