Expected

On a pre-Lollipop device (API < 21), enabling the passcode lock by switching on the Enable lock option in Settings displays the PIN input screen.

Observed

On a pre-Lollipop device (API < 21), nothing is displayed when enabling the passcode lock option. The Settings screen remains.

Reproduced

1. Tap _Settings_ icon.
2. Tap _Enable lock_ option in _Settings_.

Tested

Nexus 5 on Android 4.4.2 with PasscodeLock Sample 1.0
Samsung Galaxy S III on Android 4.4.4 with PasscodeLock Sample 1.0
Samsung Galaxy Tab 3 on Android 4.4.2 with PasscodeLock Sample 1.0