What just happened? If you happen to own both an iOS and Android device (perhaps you haven't been able to decide between the two), Google has some good news for you. Starting now, iOS users will be able to use an Android tablet or smartphone as a hardware-based security key for their Google or Google Cloud service log-ins.
To enable the feature, you simply download Google's "Smart Lock" app on iOS. Upon doing so, any attempts to log into your Google account will automatically send a verification request over to your Android device of choice.
It seems likely that there will be a few ways to verify a login request, but the default option appears to require you to hold down your Android phone's volume button for a couple of seconds.
This idea might seem a bit worthless to anyone who only owns a single smartphone (in either camp), but there are scenarios where it could be helpful. If you happen to prefer Apple-branded tablets, for example, but exclusively use Android smartphones (and carry both around with you), this makes logging into your Google account quickly and securely on said tablet just a bit more convenient.