Alcohol breath testing on a larger scale will save lives. Alcohol abuse is a major contributor to death and disease. Alcohol intake affects the human body by significantly longer response time to external stimuli. In situations where the senses need to be on alert this delay can be the difference between life and death. To make the alcohol breath test more available in everyday use, the mouthpiece has been removed. Instead, the exhaled alcohol is measured directly in a diluted sample. The dilution can be accounted for by simultaneous measurement of an endogenous tracer gas. Because of the lack of a mouthpiece several additional factors influence the alcohol measurement, e.g. the obvious lower abundance of analyte gas, shorter time of analysis and physiological aspects of the tracer gas. My studies include sensor development and validation through laboratory experiments as well as human subject studies. Several sensor parameters are crucial for the functionality of the alcohol detection system and are in need of careful investigation. Human behaviour and physiology also needs further understanding. A better understanding of the system provides vital knowledge for the design of smarter algorithms. Planning, conducting and evaluation of these studies lie within the scope of the licentiate thesis.