What is the ruling on selling alcohol breathalyzers imposed on drivers, and does the ruling differ between selling them in places where alcohol is consumed, in public places, to individuals, or in a Muslim or non-Muslim country?

There is no harm in selling devices that measure the alcohol percentage in a person's body to Muslims and non-Muslims in any country, because the default rule for things is permissibility, and selling is permissible. This device does not aid in drinking alcohol and is not a direct or indirect cause of sin. Rather, the device may serve the community's interest by protecting societies from the transgression of drunk drivers, and it may be used by enforcement agencies to deter drinkers.

As for selling the device in places where alcohol is consumed, a Muslim is not advised to enter such places unless he is an admonisher and reminder without causing discord.