With a post on the service blog Google For Work (Google Enterprise replacement) the company announced a new tool available in the security settings of your Google account.
This is the tab "Devices & activity", a dashboard that shows all devices that have accessed your Google account in the last 28 days. You can also see the device you are accessing right now.

The security measure focuses on commercial consumers of Google For Work products, but it also works for common users. The utility is apparent, if you see a device that is not yours, you will know that someone is accessing your information. If the login to your account is permanent on a device you do not know about, Google offers the option to revoke permissions to do so.
The link to the dashboard is in the security settings of the Google account in the "Recent Activity" box on the right. You can access it. click here.