This is a simple-to-use Carbon Monoxide (CO) sensor, suitable for sensing CO concentrations in the air. The MQ-7 can detect CO concentrations anywhere from 20 to 2000ppm.
Wiring example (works in Arduino too)
Part of the Muotoilun laboratoriot project.
University of Lapland
Faculty of Art and Design
Some photos from the lab and related projects (earlier ones as well) can be found here.