All our CO2 Remote Storage Safety Alarms (RAD-0100, RAD-0200, RAD-0102, RAD-0102SX2) ship with a rubber vent cover inserted into the sensor air inlet. This plug protects the device during shipping.
After installation, the vent cover must be removed in order for the CO2 Remote Storage Safety Alarm to detect CO2 levels in the ambient air. Failure to remove it will cause the device to not function correctly.
The sensor's IP65-rated case is sealed so that it can be washed down with the sensor vent cover installed. Therefore, the plug should only be inserted into the air vent when washing the sensor or spraying down the floor near the device. This will prevent water and debris from entering the vent and potentially fouling the internal electronics and the sensor.
If you are concerned about losing the plug, you can use double-sided Velcro to mount it on the side of the sensor unit, or attach it with a bit of tape and string. If the vent cover plug is lost, you should temporarily cover the vent with sticky tape before washing around it to insure that no water gets inside.