The MQ-3 Gas/Alcohol sensor is not accurate enough to use for any serious breathalyzer applications, it also needs to be properly calibrated which is a process I did not undertake. The 25 Shiftbrites are powered by a 4.5volt 500mA adapter, I'll have to check what I powered the MQ-3 with – but I recall it was the adapter from an old ZIP drive. The LCD and speaker I used are optional for this setup, certainly not required for the test-your-strength breathalyzer. Have fun and drink responsibly. *This device is no where near accurate enough to measure blood/alcohol levels.