The opening for the chain on the catch is located away from the door edge making it impossible to detach when the door is open.
How to install a chain lock on your door.
Security chains are available keyed or un keyed.
Drop the chain into it.
Tape up the template for the lock plate.
If you do not have a deadbolt on the door place it about three to six inches above the door handle.
Place the security chain keep onto the lock rail of the door opposite the chain bracket you have just fixed.
Position it about 3 to 6 inches above the deadbolt on your door.
The slide catch should be mounted close to the edge of the door.
A door chain lock is an additional lock to the standard deadbolt and door handle locks that may already be on your door.
Slide the fitting towards the centre of the door so that the chain tightens up but you are still able to lift it out when the door is closed.
Insert the exterior part of the lock into the door by feeding the long metal piece through the opening in the center of the bolt.
Keyed security chains as shown left allow you to lock or unlock the chain from the outside if you re dexterous.
Insert the new bolt into the opening on the edge of the door and fasten it to the door with the provided screws.