Android: The Smart Lock feature in Android allows you to disable your lock screen selectively based on criteria such as location or voice recognition. A recent update to this feature allows you to set geofence areas around a place, rather than only entering a street address.
Part of the problem with the old method Google used to identify location in Smart Lock is that it could only use an address. So, say you wanted to set it to unlock at work, if the address didn't register close enough to your address, you could end up locked out anyway.
The new interface, which has rolled out as part of the new Google Play Services, allows you to designate a geofence instead of an address. As long as your location is within this circle, your phone will be unlocked.
As Android Police notes, some users have seen this feature activated already, but if it hasn't been enabled for you, you can download Play Services 7.3 from Android Police's APK Mirror site here.