If you strap this device to your forearm, it vibrates when you raise your arm to touch your face. Useful? Not sure, because one gets many false positives. Cheap? Yes. Applicable everywhere? Yes.
Update 2020-03-19: I've been using it all day while working at my desk and it has warned me of touching my face several times. I got rid of false alarms while typing, mousing or handwriting by pointing the tilt switch slightly towards the outside (ulnar side) of my arm.
It consists of three main components (available from Amazon and other online retailers):
- tilt switch
- vibration motor
- 3 V battery
Plus some cardboard and tape. No soldering required. For holding this to your arm, you can use a sweat wristband or the elastic part of an old sock. Or rubber bands if you're hard up.
If you want to know details of how to build it, let me know and I will improve the design and post instructions here. (People coming from the outside can email me: <given name of President Nixon>.firstname.lastname@example.org)
- Instructables: Don't Touch Face – This is where I got the idea. It's bigger and requires more equipment.
- Do Not Touch Your Face and DontTouchFace.com web apps. – Only work when you sit at your computer.
- Immutouch – Probably fewer false positives. Takes longer to ship. More expensive if you disregard the cost of your time.
- surgical mask/respirator