It could also be used with a camera-based position detection system as shown above, meaning your finger's location and force could be calculated on a non-active surface like an ordinary table.

ENGADGET: Sony patent claims touch force detection via microphone

More signal input subsequently equals a more secure position read-out, with the elderly base system offering initial location accuracy to around 100 meters.

ENGADGET

Called "Motion DNA", the patent-pending software developed by Navisens detects a person's realistic location and position inside a building in 3D and in real time.

BBC: Technology that works behind closed doors