A simple arduino breathalyser that uses the popular MQ3 digital and analog outputs. Runs on 3.3V and 5V though a 5v supply is preffered for the heating elements of these sensors.
As can be ascertained from the datasheet of the MQ3 the breathalyzer project here is fairly simplified not taking into account temperature changes. So I wouldn't recommend for people in the tropics or Canadian mountains due to the change on resistance and sensitivity of the element.
Fork the existing project before beginning any changes to the code. Once forked begin making any changes on either the new fork or a fork of your own depenending on the methodology you're using.
A blog article was written for this project with details on its construction and use.