There are two main types of door lock: the mortise lock and the cylinder rim lock. However, additional security locks and bolts can be fitted to improve security.
A key which turns a series of levers operates a mortise lock. The levers will either withdraw the mortise latch to unlock the door or propel it into the housing in the latch-plate to lock the door. The mechanism of a mortise lock will have between two and seven levers. Remember that more levers will afford greater security, as the lock will be more difficult to pick. If you are fitting a mortise lock to a front door it should have at least five levers. A mortise lock can be operated from either side of the door and is often referred to as a deadlock.
A deadlock should never be activated or locked from the outside when people without a key are inside the property, as it would prevent them from evacuating the building in the case of an emergency.
Cylinder rim lock
To unlock and open a door fitted with a cylinder rim lock from the outside a key is pushed into the keyhole and turned. On the inside of the door there will be an unlocking lever. To open the door from the inside, simply push the lever down. Next to the unlocking lever there will be a catch that when activated deadlocks the mechanism.
Door security bolt
Door security bolts are fitted into the opening edge of the door, usually in pairs with one situated towards the top of the door and one towards the bottom of the door. A key is used to operate door security bolts.
Another additional security measure, hinge bolts prevent the door being forced open off its hinges. Once again they are usually fitted in pairs, this time into the hinge edge of the door, one below the top hinge and one above the bottom hinge.
Standard door bolt
A sliding barrel bolt is screwed to the inside of the door. The locking bar slides along the barrel into the ring screwed to the doorframe. Front doors may well have a door bolt both at the top and bottom. Standard doors bolts come in many designs, so it is easy to find one that matches the door furniture.
Surface-mounted locking bolt
This works on the same principle as the standard door bolt but allows the bolt to be locked in position for extra security.
A small length of chain that when in position, restricts the opening of the door to only a few inches and allows the occupant of the building to check the identity of the caller.
Door viewer or spy hole
Fitted into the door at head height, this allows you to see who is on the other side of the door before opening it.
Hasp and staple
A simple way of closing doors and windows. Usually found on sheds, outhouses and other property with low grade security. The two elements are usually connected with a padlock.