In Active mode the subject blows into the sampling cone until a sample is taken by the instrument for alcohol analysis – fully automatically. Within seconds a coloured light appears, with a beep tone, to indicate whether that sample contained alcohol. The system then clears itself – again, fully automatically – so that within seconds again it is ready to test the next subject.
In Passive mode the operator presses the Passive button to draw in a sample of breath from around the subject, ideally while they are speaking. Again, the display system then very quickly shows whether or not that subject has alcohol in their body. This Passive mode is also ideally suited to checking the air above fluids, to see if these contain alcohol.