People use a breathalyzer as a deterrent,  which helps them and their family / friends make more responsible decisions when they are out for drinks. The best way to use a breathalyzer is to not drive if the device suggest even a tiny bit of alcohol.

Good breathalyzers in the market try to give an accurate - enough blood alcohol count (BAC).

Remember, a breathalyzer only provides a rough estimate of your blood-alcohol content. But, an indication of aocohol in your blood stream should be enough alarm for you.

Moreover, inserting a fresh mouthpiece into the machine before every use will help to ensure a non-contaminated BAC reading.

The best personal breathalyzer: BACtrack S80 Pro (Accurate, portable, and easy to use)