Ok, this application might sound a bit odd. I am trying to figure out what kind of sensor I might use that could be used to sense when a person moves his or her hand close to their face. I need the sensors to be very small and unobtrusive to the wearer -- and, with that said, the sensors obviously have to be wearable. I am new to physical computing, so I don't know the right direction to explore.
The precision of the measurement does not have to be exact -- and, the type of data that I am ultimately looking to collect is simply doing a running count. For example, my ideal sensor would be bracelets, perhaps with embedded magnets. Then, another sensor would be connected to the persons collar or a necklace. So, assume that a person has a chronic nail biting habit. Each time the persons hand went to her or his mouth, it would log the event. Of course, this isn't precise measurement because it simply indicates whether the hand reached the general area of the mouth. And, yes, you would have a lot of false positives in the event of sneezing, scratching, and eating, but all these errors in data collection are easily managed from my point of view. Again, I am really just trying to solve the problem of identifying the event when the person's hand goes close to her or his face.
What dhenery is forgetting is the effect the body will have on the coils. This will swamp the signal you are looking for.
You can get wrist mounting RFID tags that look like a watch, it might work. But I think it is one of those projects that sounds a lot easier that it actually is.
