Four years after the debut of its entry-level environmental monitors, Xiaomi has refreshed its most accessible smart home sensor. The new Mijia Smart Thermometer and Hygrometer 3 Pro arrives with a significant functional upgrade: integrated carbon dioxide (CO2) detection. Priced at just $17 (114 Yuan), the device aims to bring professional-grade air quality monitoring to the average desktop or bedside table.
While previous iterations focused strictly on temperature and humidity, the 3 Pro addresses a growing demand for indoor air quality awareness. By incorporating Sensirion’s low-power thermal conductivity sensor, the device continuously tracks CO2 concentrations, providing a vital metric for maintaining a healthy living or working environment.
Smarter Air Quality Monitoring
Instead of overwhelming users with raw data, the device utilizes an intuitive three-color indicator system. Green, yellow, and red status lights offer an immediate visual cue regarding air freshness, signaling exactly when it is time to crack a window for better ventilation. This simple, glanceable interface removes the friction often associated with complex environmental monitoring.
Beyond basic detection, the sensor integrates into the broader Xiaomi ecosystem via the Surge Smart Connectivity system. When paired with a Bluetooth Mesh gateway, the device becomes an active trigger for home automation. You can set specific thresholds in the Mi Home app so that your smart speakers provide voice alerts if CO2 levels exceed a comfortable limit, or trigger other connected appliances to improve airflow automatically.
Design and Ecosystem Integration
The physical design has also seen a practical overhaul. The 3 Pro now features a crisp 3.6-inch LCD screen with reduced bezels, offering a cleaner look while displaying time, date, temperature, humidity, and CO2 levels simultaneously. A single tap allows users to toggle through specific data points, keeping the interface uncluttered.
Versatility remains a core pillar of the hardware. The unit can be placed on a desk or mounted to metal surfaces using its integrated magnetic backing. Powered by a single CR2450 button battery, the sensor is rated for approximately one year of operation, ensuring that users are not constantly swapping out power cells.
For those invested in long-term data tracking, the Mi Home app keeps logs of temperature, humidity, and CO2 trends over time. This functionality allows users to analyze environmental shifts over days or weeks, providing insights that are typically reserved for more expensive, dedicated air quality hardware.
