My buddy is a pilot. He was flying over Austria, ski resort of some sort, and he was talking the guy in the cockpit for about 5mins while flying above. His phone was turned off. When he landed his plane he took the paper work, then turned on his phone to continue filling the data in the app from the company, info about distance, fuel, etc. He had like 15 minutes off so he went on facebook. You know what first sponsored ad was? The same ski resort he talked about when flying over. He never googled about it before. So yeah, it's a fact phone is/can be tracked even when it's turned off, especially now when you have phones that can't take their battery out. Same shit happened to me a couple of times I talked. I was getting recommended stuff that I never googled before about it. Majority of people install apps but nobody reads licence of agreement and that stuff, everyone just auto accepts.