If asked by a law enforcement officer to take a test to determine your blood alcohol concentration (BAC):

Most states have an Implied Consent Law, which means that by driving a vehicle on the state's roads, you have agreed to undergo a drug or alcohol test if a police officer asks you to do so. If you refuse to submit to a test, you will lose your operating privileges. Make sure you are aware of the laws for every state in which you drive.
DMV Writen Test