The yale 89 series deadlocking standard nightlatch security locks are some of the most widely used front door latches they are key operated from the outside and lever handle operated from the inside the latch automatically deadlocks on closing the door and the snib function bolt hold back button enables the latch to be held back the inside handle can also be deadlocked by a reverse turn of the key in the cylinder giving additional security when deadlocked in this manner the latch cannot be opene