AlcoSense Blow Tubes are nessesary for the AlcoSense Lite, Elite, SE and Zero, but also fit the AlcoSense Excel, Pro and Ultra.
The blow tubes have a rough interior surface which helps to reduce condensation build up in the breathalyzer and improve reading accuracy. Always use a blow tube with your breathalyser, it greatly reduces the risk of saliva ingress into the blow chamber and improves the lifetime of your breathalyzer.