Using Smart Lock on Lollipop? Use this trick to manually lock in an instant

Using Smart Lock on Android 5.0 is a great way to balance security and convenience, using a trusted location, Bluetooth device or NFC tag to bypass lock screen security without entering a PIN or lock pattern. However it's possible you might not want your phone completely unlocked all the time, which is why there's a simple way to manually lock your device — requiring your PIN, pattern or password to unlock — with just a button press from the lock screen.

source: androidcentral