There is nothing wrong with selling equipment that measures the levels of alcohol in the body

Firstly: 

There
is nothing wrong with selling equipment for measuring levels of alcohol in
the body, whether that is in a Muslim country or a non-Muslim country, and
whether the purchaser is a Muslim or a non-Muslim. That is because the basic
principle concerning all things is that they are permissible, as Allah, may
He be exalted, says (interpretation of the meaning): “Allah has permitted
trading” [al-Baqarah 2:275]. 

Moreover, equipment for measuring alcohol levels does not help people to
drink alcohol, and it is not a direct or indirect cause of this sin. The
prophetic texts only forbid, with regard to alcohol, anything that may help
people to drink it, manufacture it and deliver it to those who consume it.
The Prophet (blessings and peace of Allah be upon him) said: “Allah has
cursed khamr and the one who drinks it, the one who pours it, the one who
sells it, the one who buys it, the one who squeezes it, the one for whom it
is squeezed, the one who carries it and the one to whom it is carried.”

Narrated by Abu Dawood in as-Sunan, 3674; classed as saheeh by al-Albaani. 

As
this equipment does not come under any of these headings and cannot be
likened to any of them, the basic principle that it is permissible remains
in effect. 

Even
if it is used by a driver who has drunk alcohol, his use of it cannot be a
means to help him to drink, and his not buying it can never be a deterrent
to drinking; rather the equipment will be a means of checking himself, so he
does not add to the evil of drinking the evil of driving in an intoxicated
state which may lead to harm and damage to people and property. 

We
asked Shaykh ‘Abd ar-Rahmaan al-Barraak about selling this equipment, and he
said: What appears to be the case is that it will serve a purpose, so it is
permissible. 

Secondly: 

It
may be said that it is Islamically prescribed to manufacture and sell this
kind of equipment, which protects society from the harm caused by those
sinners in traffic accidents and the like, and may be used by police forces
to deter drinkers so that they will not commit further crimes when they are
intoxicated. So use of this equipment is usually in the interests of
society, and we do not see any harm in it or anything that would suggest
that it is haraam. 

Thirdly: 

With
regard to selling the equipment in places where alcohol is drunk, we do not
think that a Muslim should go into places where these evil deeds and sins
are committed, so that it will not be a source of temptation for him and so
that he will not be recorded with Allah, may He be exalted, as being among
those who approved of or kept quiet about evil, or who condoned disobedience
towards Allah on earth, unless he goes there to advise and warn, without
causing any trouble or doing anything that would lead to a greater evil. 

And
Allah knows best.