Using magnets for surrounding-sensors
I just had this idea I thought would be nice to share:
Imagine a approximation sensor of some sort (I have not looked one up yet) attached to your finger (or wherever you think it is useful) connected with a small electro-magnet loosely attached to your finger with the implant.
In off-mode, the electromagnet would not generate any field but when the approximation sensor detects an object nearby (distance must be defined) it forces the electromagnet to generate a field which you then would be able to feel with your finger.
The energy-source for both the sensor and the electro-magnet could be realized in form of a mobile-phone battery or something.
Future application would of course be internal (implanted) energy source.
Edit: I just realized that smartphones have these tiny sensors on the top so these may be of some help. They are like 4x4x4 mm or something.