Modern Double Cylinder Lock
What is a double cylinder door lock? : Modern Double Cylinder Lock
Quote from Article entitled What is a double cylinder door lock?:
A deadbolt lock is a cylinder operated lock which requires complete rotation of the cylinder to unlatch the bolt. This means that you cannot open the lock unless you have the right key. Double cylinder deadbolt locks in particular allow locking and unlocking on both sides of the door for additional security. With this design in place, it is impossible or at the very least extremely difficult to gain forced or unauthorized access both into and out of a building.
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