This is a DIY maintenance kit for the uRADMonitor MODEL A3, containing the three sensors that wear out over time: the particulate matter sensor (fan wear or dust build-up), plus the electrochemical Ozone and Formaldehyde sensors (2 year service life). All three attach via simple plug-in connectors, replacement takes minutes with no soldering. The other sensors shown (CO2, temperature, pressure, humidity, noise, VOC) are soldered on the board, have a much longer life and are not included. Fits Model A3 hardware version 10 and above only, as the current PM sensors do not fit older boards. Unsure of your version? Contact us with your device ID.