Low power detection of known objects (magnets?)

Hi folks,

I'm trying to avoid touching my face, and devised a plan to create a pendant that detects when my hands get near my face. I had some other ideas too for what approach to take, but put them on ice. (0)

My initial plan was to wear bracelets with neodymium magnets, and then having the pendant around my neck beep when the hands/bracelets get within a few inches.

Ideally, the whole pendant would be super low power and as small as possible. My initial idea was a Reed switch for that reason. However, upon some research it seems that range may be way to low, and I'd have to get very near for it to detect the magnets. I then started looking at magnetometers and hall sensors, but they seem to take more power + may be affected by magnet orientation and the like.

My current plan is to buy some hall sensors and magnetometers and just experiment a bit and see how things work out.

However, to save some time and money, I'd love to hear what y'all suggest first. Which of these approaches make sense to you? Any alternatives you'd suggest?

Main criteria:

  • Low power
  • Range of 8+ inches
  • Range measurement isn't important - a simple "is the magnet around yes/no?" boolean answer is fine.
  • Entire system ideally last 16h+ on battery

Now, this may have an obvious solution. This may not be possible given the constraints. Forgive my ignorance and please let me know if this isn't doable. If you have a better approach, I'm all ears!

Thanks!

(0) Other ideas:

  • Orientation sensors on bracelets - detect when wrists become vertical. (More expensive? High power usage? Lots of false positives maybe when reaching for things?)

  • RFID reader with RFID on wrists. (Poor range? High power usage?)

  • Sonar sensor (False positives? High power usage?)

Google some of your sensor ideas , see what is available and what the specifications are .

Personally I use a short piece of string - one end tied to my belt, the other to my wrist.

Have you considered a short range distance sensor? there are many as large as a wrist watch

hammy:
Google some of your sensor ideas , see what is available and what the specifications are .

Personally I use a short piece of string - one end tied to my belt, the other to my wrist.

hahaha. I like the way you think! But what do I do when I get tangled in the string? I guess I won't be touching my face at least...

humandroid:
Have you considered a short range distance sensor? there are many as large as a wrist watch

By "short range distance sensor", do you mean ultrasonic/sonar like HC-SR04? I was concerned about battery usage and false-positives, but have no experience using one...

norsktorsk:
hahaha. I like the way you think! But what do I do when I get tangled in the string? I guess I won't be touching my face at least...

Be more worried about the other end of your body!

Paul