Simply turn it on, breathe into the sensor for a few seconds and a reading appears on the digital display within 5 seconds. Unlike many similar priced models available in the UK, this device is extremely accurate and displays the precise BAC (blood alcohol content) reading on screen in 0.01 increments rather than simply giving you a wide band that your reading is in. This updated model now comes with a handy red LED backlight for easy reading in dark conditions, and being only 9.5cm long it's small enough for you to keep in your handbag or pocket for when you need it.