Every 8 days, the device performs the calibration process automatically. 
No maintenance is required. 

You can also manually calibrate the CO2 sensor: 

1. Place your OPEN'R product near an open window for at least 2 minutes. 
2. Press and hold the button on the back of the sensor for 5 seconds. 

The orange LED on the back of the sensor will be steady for the duration of the calibration. Then it turns green for 5 seconds when calibration is complete.