The Net Safety M21 Millennium II is a single-channel universal transmitter engineered for reliable operation in extreme conditions. It supports a wide range of toxic and combustible gas sensors, including SMART sensors that are pre-calibrated and automatically recognized by the transmitter. The transmitter continuously communicates digitally with the sensor, ensuring stable, accurate readings even over long separation distances (up to 2000 ft).

The M21 Millennium II features a full graphic OLED display readable in all lighting conditions, with text menus in English, French, Portuguese, or Spanish for simple setup and calibration. It offers multiple communication protocols, including HART and THUM WirelessHART adapter compatibility. The transmitter operates from -67 to 185°F, has the lowest power consumption in its class, and includes full diagnostics with event and data logging. For combustible gas detection, it uses poison-resistant catalytic bead technology with SensorGuard and infrared sensors with a dual-beam design.