Google has been informing its users of any logins for quite a while now, but this notification is only available via e-mail. That is no longer the case though as Google has decided to inform you about any account logins via Android notifications as well.
Much like the e-mail option, your Android phone will now inform you if you have logged into another other device besides the devices that you currently have. When the notification pops up, you’ll be able to review exactly which device has logged into your Google account and the location where the login was made. Should anything appear out of the ordinary, you can then change your account credentials on the spot, allowing you to react almost immediately.
This feature is currently being rolled out to users. Google notes that it may take up to two weeks for some people to receive this new feature. That said, this notification will be highly useful to those that do not check their e-mails all that frequently.
Source: Google Apps Update