But a faraday bag cuts off all radio communication right? So no phone signal, Bluetooth, WiFi or GPS. Any audio and video would be incomprehesibly muffled by the bag. And the phone isn't being actively used while in the bag. So what info is left to send at that point?
Discussion
Audio might be better than you think, maybe good enough to analyze later in the data center, along with accelerometer and gyro and maybe barometer data etc, to try to get some location guesses, or at least an estimated maximum possible distance traveled.
Researchers have shown a laptop microphone can tell what a user is typing on the keyboard (without access to the keyboard input) - never underestimate what a few scraps of data can do