UPDATE: See the end of the article for information on how to delete and disable much of Google's tracking information
Is your mobile device spying on you? It may be doing just that! Let's look at the two major mobile arenas, Apple iPhones and Google Android phones.
Apple explains how Siri listens for "Hey, Siri" without eavesdropping and how it keeps Siri usage anonymous. Siri uses a buffer, or a chunk of audio that's continually recorded over, to listen for the "Hey, Siri" trigger phrase. Once the trigger is heard, it records the user's question or command. This recording is sent to Apple with an anonymous identification number that isn't tied to an individual's Apple ID. More on the Apple story here: https://nakedsecurity.sophos.com/2018/08/13/siri-is-listening-to-you-but-shes-not-spying-says-apple/
Google wants to know where you go so badly that it records your movements even when you explicitly tell it not to. An Associated Press investigation found that many Google services on Android devices and iPhones store your location data even if you've used privacy settings that say they will prevent it from doing so. Computer Science researchers at Princeton University confirmed these findings at the AP's request. More on this story is here: https://www.securityweek.com/google-tracks-your-movements-it-or-not
The bottom line - check your device's privacy settings, both overall and on a per-app basis. Set them to levels that you feel comfortable with. If you find that the app doesn't adhere to your settings, complain to the app's authors and consider using an alternate app that provides a similar function.
UPDATE: How to Find and Delete Where Google Knows You've Been
The first thing to do, regardless of device, is to login to myactivity.google.com and go into "Activity Controls." Disable "Web & App Activity" and "Location History" to stop Google from storing location markers on your Google account. Some services won't work well (or at all) without these features, such as Google Assistant or a Google Home speaker. Additional details are in this AP News article: https://www.apnews.com/b031ee35d4534f548e43b7575f4ab494/How-to-find-and-delete-where-Google-knows-you%27ve-been