The "passive" is the one that you state your name into (mouth presence? but speaking air comes from the lungs....?)
THe next one is the screening test - blow into the mouthpiece - ie: lungs again.... which is an indication of where your level will be (fail general = over 400, fail youth over 150 - under 400 and pass is fine - under 150....)
The machine is the eveidential one, which gives an actual reading of your breath alcohol level.
As for the ones you can buy, they would not be any defence if you passed on it and got stopped just down the road and failed on the "gazetted/approved" devices.
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