This is not extremely new technology, but not a lot of people know about it and it has evolved quite nicely in recent years. Sensitive Object is a French company that sepecializes in the use of microphones to detect touches anywhere on an arbitrary objects. With multiple mics they can determine the location of touches or even dragging (as well as multiple dragging touches - not shown in the video below).
I've had a chance to play with it in person, and it's pretty impressive stuff. It works a lot better than I would expect. It doesn't detect touch locations using a triangulation technique (i.e. see how long it takes for the sound to reach each microphone) because that would vary greatly depending on the material the object was made of (plastic, metal, wood, etc) and depend on the shape of the object. Sensitive Object can do any shape like a vase, or statue.
They accomplish this using a pattern matching technique. Each touch sound gets compared to a known table of sound-to-location mappings. Which means you have to enter this mapping during a calibration step. (i.e. give the system a couple examples of touching each location that you want to recognize, touching here sounds like this.... touching there sounds like that). This upfront calibration step is somewhat heavy, but when you are done it's quite powerful. You could turn a cardboard box, a basketball, your car, or even your friend's head into a touch sensitive surface (if it's hard enough). Though, larger objects may only be "bang sensitive" surfaces.