Don't get behind the wheel without the Portable Breathalyser with LED Indicator Simply blow into the mouth piece on top for up to 5 seconds to get a reading LED traffic light system shows if your reading is safe: Green light: Safe, alcohol concentration level is under 0.02% BAC Yellow light: Caution, alcohol concentration level is 0.02% to 0.05%BAC Yellow and red light: Danger, the alcohol concentration level is over 0.05% BAC Keychain design makes it easy to keep on your ready for when you drive Measures 72 x 39 x 18mm Requires 2x AAA batteries (not included) Save 88% and put it to the test with a Portable Breathalyser with LED Indicator