Replying to cbr/muro - those are emails about specific people that you have allowed to see your location data. The NC police are getting warrants for everyone in an area's location data. It doesn't matter if you've shared it - GPS, cell-tower data is passively collected by Google and then provided en masse to the police when subpoenaed. Nobody receives periodic emails from Google saying "you have your location services turned on [which we will nag the shit out of you about if you don't] and thus Google has a running log of everywhere you go [and if you happen to be in a jurisdiction that wipes it ass with the Fourth Amendment we'll also turn over all the data we've collected to the police]."
You can go into your account settings under Personal Info and Privacy\Manage Your Google Activity and toggle your location history if you want to turn it off, but I've never had them update me via email. Given how much information is in that, I'd be surprised if they prompted anyone to go review it since most folks would likely feel like it's creepy to see a map of everywhere they went.
Subject: You are using Google Location Sharing to share your real-time location.
Hi Jeff,
To protect your privacy, we would like to remind you that you are sharing your real-time location using Google Location Sharing with [wife] and [close friend and housemate].
If you didn't enable this or want to stop sharing your location at any time, please go to your Google Location Sharing settings.
Sounds like this is a reminder that you're sharing your location history. People who just have it on (which means, "just" sharing with Google), do not get these notices.
