This Breathalyzer performs gas detection through a sensitive semiconductor sensor. This portable breathalyzer can quickly give a referenceable result when the result is + or - 0.02 sensor accuracy at 0.050 percentage of BAC. 2AA 1.5V batteries need to be prepared before use Press the button for about 2 seconds and the device will turn on, then the device will count down from 20 seconds. When the countdown is over, the screen will display "". then blow evenly until the device emits three beeps, and the test result will be displayed on the screen after a few seconds. All test results are shown on the LCD display, including the battery level, and alerts are given when the battery is low. In addition, there is an automatic shutdown function, when the Breathalyzer is turned on, if 20S no operation will automatically shut down to save electricity. Breathalyzer is only 4.84in x 1.73in x 0.75in and supports 2AA batteries. You can carry in your pocket, bag or in the car. Very convenient to carry out. Package: 1 x alcohol tester, 1 x manual, 5 x Mouthpiece, Warm Tips(No Battery) Power Suplly:2 x AA 1.5V batteries(Not included batteries) Colour:Black Material:ABS Package Contents: 1 * alcohol tester 5 * Mouthpiece 1 * English manual Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.