People who have long commutes on public transit will know all about the subway sleeping phenomenon, which is where this Google Now application comes in. Using the app turns your smartphone into an alarm clock that will ensure commuters wake up before their stop.
Even if you aren't a chronic subway sleeper, it can be really easy to drift off if you're using public transit to get home late at night after a party or after a particularly long day. The Google Now application turns the intelligent personal assistant (which works through the Google Search mobile app) into an alarm when you open the extension on public transit. This can be done through an iOS or android device, as well as through the Chrome browser on a computer.