The Truth Meter, a project featured in MAKE Volume 26, measures small increases in sweat which indicate nervousness and other stimuli. So if you’re sleuthing to find out who left the empty milk carton in the refrigerator and your prime suspect does nothing but deny accusations, watch this video and create your own Truth Meter.

For more information about this project and a PDF of the instructions from MAKE, check out:

Here’s a kit with the components you need to build your own: