The above method works only for web browsers and as you can guess, this excludes mobile browsers and mobile apps. This also means that if you use an Android handset and it’s been stolen, or you left your phone unattended and unlocked, someone, anyone, can access your email. To sign out of Gmail on your Android phone, you need to take more drastic measures. You will have to revoke your phone’s access to your Gmail account. Head over to your Google Account Settings and go to the Security tab.
Under Account Permissions, click View All and wait for the list of apps, services, and devices to load. Your Android device will be listed here and when selected, you will see a Revoke Access button. Click it and your Android device will no longer be able to sync email, contacts, etc. Be warned that if you’ve lost your Android phone, revoking access to it like this is not a good idea if you plan on trying to lock or find it.