US Patent 9674625 Passive proximity detection

Techniques and devices are disclosed for utilizing passively received audio signals to determine proximity of devices to other objects. In one embodiment, a method of passive proximity detection is provided that includes sensing a first sound wave using a first audio transducer and generating a first signal representative of the first sound wave. A second sound wave is also sensed and a second signal is generated. The method includes comparing characteristics of the first and second signals using a processor to determine if differences between the first and second signals indicate the first audio transducer is proximately located to another object.