Using a thermostat is an eco-friendly way to control indoor climate. Young engineers practice building electric circuits by designing and constructing a thermostat. Plenty of background information, a vocabulary list, links to the worksheets, and more are provided. The procedure is written as a paragraph within the lesson plan, rather than in numbered steps. The lab sheets, however, have clearly delineated steps. This is a comprehensive and practical activity to use with engineering or physics classes.