Praise be to Allah.

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.