Google’s Smart Lock feature for Chromebooks lets you unlock your notebook automatically when your smartphone is nearby.
You’ll need a phone running Android 5.0, a Chromebook running Chrome OS version 40 or later, and support for Bluetooth on both devices.

Google first unveild the Smart Lock for Chrome last summer, but the Chrome team announced that it’s now available in the stable channel of Chrome OS.
Smart Lock will let you log into your Chromebook without entering a password, saving a bit of time. Since this only works when your phone is near your laptop, it should prevent unauthorized users from accessing you data.
In order to sign into your Chromebook, your Android phone will need to be within Bluetooth range (about 100 feet) and you’ll need to unlock the lock screen on your phone.
Nice to have options, but it’s quicker for me to unlock my laptop than it is to unlock my phone (especially if phone is in my pocket). It’s not really unlocking without entering a password, unless one has their phone always unlocked (a bad idea).
In fact the reverse would be more useful – keeping my phone unlocked if my laptop is unlocked and nearby…
ChromeOS should be version 40, not 4.0.
My G Watch unlocks my Nexus 5 which unlocks my Chromebook. Yet during the day, the N5 sometimes asks for my pin again. Talk about needy…..