The feature, now being rolled into Firefox and Internet Explorer, will flag GMail log-ins from multiple locations and flash the following warning to an affected user:
"Warning: We believe your account was last accessed from...[location and IP address]"
According to GMail engineer Erwin D'Souza, GMail will also provide more details on logins in an account activity window:
This provides a look at all GMail log-in activity over a recent time period and lets the user know whether the account was accessed by a regular Web browser, a mobile device, or via POP3 or IMAP. It also provides a quick glance at the user's current IP address to help match up against possible suspicious log-ins.