Fortunately, NASA’s Jet Propulsion Laboratory has a solution. The lab has designed a pendant that, when worn as a necklace about 6 inches below your chin, will vibrate to warn you if your hand gets too close to your face. The pendant consists of simple, affordable components housed inside a 3-D-printed shell. NASA has also made all the instructions to create it available for free, in the hopes that it might be refined and widely distributed.
More information, including a link to the open source information needed to make your own, is available on NASA’s website.