The email reminders I get look like:

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.

Thanks,

Google Location Sharing Team

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]."