Gas instruments and air instruments detect, monitor or analyze gases present in an environment. Detectors sense situations outside normal operating parameters and are set to alarm when these conditions are violated. Monitors are also set up to alarm, but their role is to determine which gases are in the stream being measured, and in what quantity they are present. Analyzers provide a breakdown of what is found, log the information, and can download it to a computer where further analysis and record keeping can be performed. Gas instruments and air instruments can sense sometimes just one gas or else can sense multiple types of gases with one instrument.