If you notice changes in your recovery email account, phone number, location sharing, etc. Also, look out for third party websites where you logged in with Gmail, especially if you used your credit card to buy something there. These can be other Google services, like YouTube, Google Photos, Google Drive, and other linked Gmail accounts. If you get notified of a log in from a device you can’t recognize, confirm it is not you and block this device from accessing your profile.
First of all, Google always notifies you of a new device logging into your account, showing its location.
