This is the fourth Alcosense One Digital Breathalyser I have bought, one each for my two sons, one for a friend and most importantly one for myself. As a driving instructor, I can take no chances with being over the limit the morning after. This instrument eliminates that possibility and can also be used on any pupil who I suspect of having been drinking. Probably breaches some "Health Police" laws on mouth hygiene, but better that than no job or driving licence!!!