This is a good thing to keep in your glovebox, to check your blood alcohol level before you put in the ignition key. I understand that the BAL varies by state, but in our area you are considered impaired if your BAL is .08% or higher. For your safety, and the safety of others in our car and on the road, if you drink alcohol, check yourself before you drive. It is also good for checking your designated driver's ability to drive.
It is small, easily carried in pocket or purse, easy to use, hold TEST button until the 10 second test begins, then BLOW BLOW BLOW, It measures alcohol level like law enforcement does.
Don't drink and drive!