I know at least one group that has used mobile-phone ultrasonics for sonar imaging of breathing. <a href="http:&#x2F;&#x2F;apnea.cs.washington.edu&#x2F;" rel="nofollow">http:&#x2F;&#x2F;apnea.cs.washington.edu&#x2F;</a><p>In terms of entropy, breathing rate is a lot of information: several breaths per minute. So if something of that rate can be noncooperatively recovered, the claim in your comment about cooperative recovery is dubitable.