WHITCO SECURITY DOOR LOCK

The lock on the front security screen door has a 'dual select' mechanism
when turning the key in the lock.

- Turn key 1 click for privacy/normal locking
- Turn key 2 clicks for deadlocking. 

When turning the key slowly to lock the door, the first 'click' indicates 
privacy mode. This is the same as turning the snib on the inside of the door 
to lock the door. The door cannot be opened from outside, but the door can 
still be unlocked from inside without a key, by turning the inside snib back 
to the unlocked position.

However, if the key is turned further, a second 'click' indicates deadlocked 
mode. When the lock is deadlocked, the door CANNOT be unlocked without the key.
A key is needed even to open the door even from inside.