Well, this is a little unsettling: it turns out that Wi-Fi signals are slightly affected by people breathing, and with the right tech someone could pinpoint where you are in a room from afar using just Wi-Fi.
This was discovered when University of Utah researcher Neal Patwari was looking for a way to monitor breathing without using uncomfortable equipment. If you can track breathing using just a Wi-Fi signal, it'll make sleep studies easier for both researchers and subjects. And it worked! By laying in a hospital bed surrounded by a bunch of wireless routers, they were able to accurately estimate his breathing rate within 0.4 breaths per minute.
Now that this is known, it's only a matter of time until there's a way to detect people in rooms using Wi-Fi signals. But don't worry! If you're nervous, there's a simple solution: stop breathing.
Via New Scientist