A Passive breathalyser analyses a sample of ambient air from around its sample inlet (spigot). If the operator has provided adequate instructions and conducts the test correctly (this requires training), a Passive breathalyser collects a sample of the subject’s breath, mixing with some ambient air, analyses this sample and determines if any alcohol is present or not. Any significant external air flow, from wind outdoors or fans/air conditioners indoors, can interfere with the sample to be analysed. If the operator is well trained, conducting a valid passive test is generally as simple as shielding the test from excesses wind, etc. by turning your back to the wind, ensuring the subject is close to and blowing or talking directly to the instrument inlet.