In this year's #nanowrimo story (which I sadly had to abandon), a virus is spread from handset to handset over inaudible sound because they've got always-on microphones. When I started writing, I wasn't sure how plausible this was going to be, but now I see that a bunch of phones - the Moto X, for example - actually do have always-on microphones waiting for voice commands. Which means that my out-there plot about phones as stealth listening devices - and the potential to hack the surveillance state by subverting that information channel - isn't so far-fetched after all. I might go back and write it properly.