Interesting tangent to this is that Google has recently announced that they are shutting down their "Timeline" service in favor of having that information stored locally on the user device. I wonder if this is a "do no evil" reaction to geofence warrants -- if Google does not have the information they cannot give it to law enforcement. This has been Google's practice in other situation (GDPR) where retaining information inherently exposes Google's customers to law enforcement violations of their privacy via Google itself.