A breath alcohol test is an estimate of your blood alcohol concentration (BAC). The test measures the amount of alcohol in the air that you breathe out (exhale). You can measure your own breath alcohol level with a simple handheld device. If the device is calibrated and used according to the manufacturer’s directions, it can provide an accurate estimate of your blood alcohol level. The home device is similar to, though not as precise as, the type of test used by police for suspected drunk drivers.