Your siblings might have eaten your Thin Mints and they all claim they didn’t, but you are sure one of them did. A real lie detector can cost a lot of money and would not be practical for only situation like this. This DIY arduino polygraph costs less than $25 and is easy to use and you can find out who is telling the truth and who did afterall, eat your Thin Mints.
The project is a DIY arduino polygraph. It measures your galvanic skin response which is an electrodermal response from the skin. Your skin momentarily becomes a better conductor of electricity when either external or internal stimuli occur that are physiologically arousing. There is a piece of tin foil with velcro around it that goes around the fingers of the subject. When the subject gets nervous, their skin will be a better conductor of electricity and the conductivity will be sent to the computer where it will be sent to the Arduino IDE program where the data will be interpreted and sent to the Processing 3 application where it will be graphed. A spike in the graph means a spike in conductivity which means the subject is nervous.
You will need:
Arduino Duemilanove (This should work with other arduino boards as well)