I wouldn't say the sky is falling, but it won't be long before this tech is ubiquitous, tech being what it is. And since it can be used for good, like checking on the elderly (I've fallen and my router is telling you I can't get up), there will be plenty of reasons for pushing the technology.
Scientists from Carnegie Mellon University have shown that an off-the-self Wi-Fi router can not only tell where you are in a room, but it can also determine your body position.
The team didn’t have to spend big to get the hardware for this experiment. All they needed was a pair of entry-level routers that cost about $30 apiece. The routers were set up at opposite ends of a room, and a computer measured 2.4GHz signal transmission between the access points.
Technically speaking. Anything that emits any sort of waves electrical or otherwise. Could at least in theory be used to spy on someone’s physical location
The caveat is. Some waves are inherently more useful for the purpose then other ones.
That and there’s faster, safer and cheaper alternatives then solely relying measuring waves.