US Patent 10519692 Door latch

A lockable spring-biased latchbolt in some embodiments of a door latch is manipulatable from a first side (protected side) of a door by translation to an opened-door position, and a separate element situated alongside the latchbolt is manipulatable from a second side (less protected side) of the door to contact and move the latchbolt to the opened-door position only if movement of that second element is not prevented by a locked position of a locking means. The locking means in these embodiments does not interfere with opening the door from the first side. The locking means can be changed back and forth between its locked position and its unlocked position by use of a key (or combination or code) from the second side of the door, and optionally from the first side of the door with or without the key (or combination or code).