If you used a public computer at a library or checked your e-mail at a friend's house but forgot to sign out of your account, Gmail has a
feature that lets you sign out remotely.
At the bottom of your inbox is information about the time and location of the last activity on your account. Click "Details" to see when your
mail was accessed using a Web browser or mobile device, the IP address from which it was accessed, the location and log out.