A breathalyzer is a tool that measures the level of alcohol in a person’s breath.
It uses that information to gauge how high a person’s blood alcohol level actually is.
These are most commonly known for being used by police on suspected drunk drivers.
But there are also varieties that are sold to civilians that can be used for party show-off or testing themselves before deciding whether to drive or not, or for people who have had a DUI, often times a breathalyzer will be attached to the vehicle and required to pass before it starts…or keeps running.