Oase biOrb Spare Automatic Misting Unit – NEW model for 2019+ units.The biOrb Air Terrarium features a built in microprocessor and humidity sensor which controls the humidity by activating the ultrasonic automatic mister in the top reservoir as required. The water level in the reservoir is detected by a sensor on the ultrasonic mister, when this drops below minimum level a signal is sent to the microprocessor which activates the low water level indicator. The sensor uses electrolytes in the water as a way to detect the water, helped by the use of biOrb HumidiMist in the unit. When the sensors detect this, it automatically triggers the misting system inside of the Terrarium.The acrylic unit is easy to replace as it slots neatly into the top of the biOrb Air Terrarium.Please check the underside of the misting unit you are replacing. This unit has a clear circle piece on the underside that clearly shows a green board. If the misting unit you are replacing does not have a green board, you’ll need the older version.