The idea is to use 3D data from the accelerometer to recognize text, written in a pen mode with the finger in the air. Z axis (or Y, in this case) can be used as a pen up - pen down flag.
I wonder if I can train the µC to resolve the character input with the low enough error rate, but I hope that this can be used for some unusual applications, or as the secret communication device.
Of course, accelerometer chip can be placed on some smaller PCB, in a kind of a ring, or so.