After several years of testing, Google is still ready to roll out a very useful (in terms of security) refinement to the Gmail mail service: this is tracking open sessions and full statistics on the connection history to your account.
Tracking open sessions works like this: if you forgot to log out of your mailbox on one computer and logged in from another computer, a warning appears indicating the IP address of the “forgotten” session.

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At the same time you can finish the session in remote mode. In some cases (if you worked in an Internet cafe and turned off the light there), it really allows you to protect your data from another computer by ending the session remotely.
That's not all. If you click on the “Detais” link, then Gmail shows detailed statistics on the types and IP addresses of the last connections to your account: IP addresses and protocols used, as well as the exact time of entry into the mailbox.

Thus, you can make sure that no one except you used the account.
In the official blog, the Gmail developers
write that the monitoring system is designed for the new version of Gmail, it continues to be tested and is not activated for all accounts yet.
via
Google Operating System