The Public Laboratory for Open Technology and Science (PLOTS) has developed an inexpensive, DIY “thermal flashlight” that you can build into an old VHS tape case. Paired with a camera, the device lets you create a color heatmap of interior surfaces. This post on the PBS Idea Lab blog describes the early history of the tool’s development. And now a school program in Harlem, New York is planning to use the device to document apartments that require better insulation.

Here’s how to make one. The thermal flashlight uses a $14 non-contact infrared thermometer that reads temperatures from short distances. It translates the readings into colored light that shines back onto the test surface from an RGB LED: blue for cold and red for hot. To make a heatmap, you take a long-exposure photograph in the dark as you sweep the flashlight over all of the surfaces you want to image. For best results, wear dark clothing, and of course stay out of the way of the camera’s view of the RGB LED light.

From New Scientist, photo: Jeff Warren.