This is a range of small digital instruments designed to measure toxic gas levels and to warn when pre-set levels have been exceeded. The development of the Responder range was carried out on behalf of MSA Inc. of Pittsburgh PA. They wanted a unit that was simpler, easier to use and, most of all, less expensive to manufacture than their existing product. The Responders have considerably better functionality, a more expensive appearance and easier manufacturing. They are also very cost effective to manufacture. Sales are considerably above the original projections.