Let me give you something else to wonder about:

Given that things ranging from toothbrushes through shoes to headsets are broadcasting or reflecting radio waves, how many receivers hidden in plants, furniture, and garden gnomes does it nowadays take to construct with entirely passive surveillance a model of the goings-on within an average house or office building? (-:

Wait til you hear about the information that a single WiFi emitter's signal strength gives you:

http://rfpose.csail.mit.edu/

Pose estimation gives you a body standing in the bathroom. Recognizing the Bluetooth signal of the toothbrush gives you what that body is doing. (-:

I also looked into that and found that it extracts some metrics from it that will get stored in a cloud service called "Aurora".