Smart Alarm FunctionWhen your test result is 0.05% BAC (or 0.25mg/L) or more, the ''Danger'' symbol will be displayed on the screen. LCD screen with a beep sound. When your test result is less than 0.05% BAC (or 0.25 mg/L), it only displays the "Caution" symbol without an audible alarm alert. Breath alcohol tester with backlit LCD screen for easy viewing of the test result at night. One Button to TestThe breathalyzer is extremely easy to use. Just insert the three AAA batteries, press the power button for 2 seconds to activate the alcohol tester, perform a 15 second warm-up, blow into the breath inhaler for 5-10 seconds, the Blue backlight LCD display shows the test result directly. The operation steps will show on the alcohol tester LCD screen, you just need to follow the prompt. 3 Unit of MeasurementYou can change the unit by pressing a button , There are 3 unit measurements to choose from, %BAC, BAC, Mg/L, when you have been drinking, it is recommended to wait 20 minutes before doing tests, this is because 20 minutes is approximately to alcohol in Blood of digestive organs.Please wait at least 3 minutes to start the next test after the last test. LCD Display ScreenAlcohol tester with semi-automatic sensor technology -advanced driver, you can get the accurate blood alcohol concentration, then judge whether or not it can drive. Thanks to the blue LCD screen, it is easier to read at night and gives you professional precision for safe driving. It will shut off automatically to save power after finishing the test for 20 seconds. 20 Replaceable MouthpiecesThis alcohol tester comes with 20 replaceable mouthpieces which can be cleaned and recycled. The 5 mouthpieces are hidden on the back of the device, just above the battery compartment! Alcohol Tester is small enough to keep in your car, purse, backpack or briefcase. especially we have prepared a portable bag in your car and a perfect gift for your friends.