Mechanisms
In order to be able to pick a lock it is helpful to understand how the lock works. The main types of lock which will be discussed here are Warded, Pin tumbler, Wafer/Disc Tumbler, Lever and Combination.
Before discussing how the different types of locks work I will first explain the basic parts of a lock and provide some other information which should help readers to understand the explanations given.
The simplest of all locks to pick and to understand is the warded lock, which is where I shall start.
Warded Locks
The warded lock is of a relatively simple design.
The diagram below shows a simple warded lock with a correct key in place. It can be seen from the diagram that the key has a number of cuts in it to allow the key to pass the protruding pieces of metal. These pieces of metal are the actual wards of the lock and will vary in length and position.
This type of lock has one or more 'wards' which prevent the incorrect key from throwing the bolt. Wards protrude inside the lock preventing a wrong key from turning and therefore from operating the bolt.
The warded lock can be found in many forms. The diagram below shows how a warded padlock works. These are usually the cheaper priced padlocks.
Only the correct key will open the lock due to the wards which restrict an incorrect key from turning within the lock.
When considering how this type of lock works it is important to remember that the wards do not move in any way and are simply protrusions along the keyway to prevent any key apart from the correct key from turning inside the lock and thus moving the bolt.
Pin Tumbler Locks
The inside of a pin tumbler lock can be seen from the diagram below.
The pin tumbler lock consists of pairs of bottom pins, which are usually made of brass, and top drivers constructed from steel. In the majority of locks there will be five sets of these pins and drivers.
When the correct key is inserted into the lock the point at which the top drivers and bottom pins separate will be brought to the same position. This position is called the shear point or shearing line. When this point is reached the cylinder will be allowed to turn and the lock will open.
The lock below has had a wrong key inserted. It can seen that the key has failed to raise some of the pins to their correct height and has also raised some pins too high. Therefore, the cylinder is unable to turn.
Many high security locks use mushroom or spool pins in order to make picking this type of lock much harder. This can be shown from the diagram below.
Pins of the shapes shown above increase the difficulty of picking pin tumbler locks as they give the impression, when picking the lock, that the pin has been picked. In actual fact the pin is still preventing the cylinder from turning but the recess of the high security pins allows the cylinder to turn slightly, giving the impression that that particular pin has been raised to the correct height.
Wafer Locks
The wafer lock is found on desks, filing cabinets, some coin operated machines and on doors of cars. Although similar in appearance to pin tumbler locks their internal mechanism is very much different.
The diagram below shows the inside of a typical wafer lock.
The wafers or disc tumblers are simply metal discs with a rectangular hole in the centre. Within a wafer lock there are usually around five of these discs depending on the security of the lock. When the key is inserted into a wafer lock it will pass through this rectangular hole.
Located on the side of each disc is a spring. The wafers will lock as the spring will force this disc down through the bottom of the cylinder and into the outer casing of the lock. Therefore, the key's function is to raise each disc out of the casing so that the wafer is instead in the centre of the cylinder. If the key was to raise a wafer too high the cylinder would also be unable to rotate as the disc would protrude through the top of the cylinder instead.
Wafer locks may be one of two types, either single or double sided. Double sided provides far more security than a single sided lock and can be found on automobiles.
The discs of a double sided lock will protrude through both the top and bottom of the cylinder. This is because the discs will be arranged with the first wafer with the spring forcing it downwards. The second wafer's spring will force it upwards. The third will be forced downwards. This alternating arrangement continues depending on the number of wafers in the lock.
The double sided lock can be distinguished from the more common single sided lock as the key will have notches on both sides of the blade.
Lever Lock
This type of lock consists of usually four or five levers. A typical lever can be seen below.
Each lever is lifted to a different height by the key which allows the notch in the lever to align with the post of the bolt. The key continues to turn and therefore moves the locking bolt through the notch where it finally comes to rest in the second gate, the key having rotated 360 degrees.
This type of lock comes in mainly two forms. Each is operated with a different type of key. Many door locks used in the UK for instance use a bit type key. Whereas lever locks found on lockers, suitcases, and desks use a flat type key, however, the principle behind each type is the same. These two types of keys can be seen at the top of this page.
Combination Locks
Combination locks appear in a number of forms and are mainly found on padlocks and brief cases. The lock may be of a dial design similar to the type of lock on a safe, or may consist of a number of small disks each with numbers on them, and having to be placed in a certain order for the lock to open. The combination lock may also be of the push button variety as found on a number of padlocks.
Although the principle behind the three styles is the same, i.e. lining up gates of various parts of the lock in order for the bolt to move, the design of the types are different and will therefore be discussed separately.
The Dial Combinaton
This type of combination lock consists of a small dial on the face of the lock and will usually have some sort of a mark or arrow on one side. This arrow is used to point to the various numbers located around the edge of the dial. In order to open the lock the dial will need to be turned several times clockwise and anti-clockwise alining the arrow with a different number each time until the lock finally snaps open.
Inside this lock are a number of discs, usually about 2 depending on the amount of numbers in the combination. On each disc there is a small notch or gate cut from it. The purpose of this gate is that when the dial has been rotated in the correct sequence, the bolt which will be holding the shackle in place will be allowed to move into the gap provided by these gates therefore freeing the shackle and allowing the padlock to open. The diagram below shows inside a typical combination padlock of this type with the front removed, where a disc and bolt can be seen in place.
On the surface of the disc to the back of the lock will be a small protrusion which will catch a similar protrusion on the underside of the second disk. The second disk will also have a small protrusion on the face of it which will catch on a protrusion located on the back of the dial. When the dial is rotated the protrusion on its underside will come into contact with the protrusion on the first disk thus rotating it. This will inturn rotate the second disk as the protrusion on the underside of the first disk comes into contact with the one on the face of the second and thus moves the two as one. When the dial is being turned in the correct sequence the disks will be turned only the right amount in order to line the gates in each disk with the bolt allowing it to move out of the shackle and opening the lock.
There are two main types of dial padlock which can affect the way in which it will be picked, which will be discussed later. The way in which they differ is how the bolt locking the shackle is constructed. Many of the older padlocks of this type could be snapped shut once open after the dial had been turned, even though the position of the gates were no longer at the same point. This was due to the bolt having a spring loaded part to it, as in the diagram above
This meant that once the lock had been open and the dial rotated rearranging the position of the gates and therefore moving the bolt back in line with the shackle, the shackle could be pushed downwards moving this spring loaded part inwards which would then spring back outwards into the notch in the shackle thus locking the padlock.
The new syle however, does not use this spring loaded part to the bolt which is instead completely solid. Therefore, when the padlock is open and the dial rotated the bolt will be forced out of the gates, and the padlock will be unable to be pushed into the lock.
The Disk Combination
This type of combination is found on a number of bicycle chains and brief cases and also on some types of padlocks, see below.
The diagram shows this type of lock in its most simplest form, a simple bicycle lock, however the principle behind this type of this lock applies to all locks of this design given a few added differences in their construction here and there.
The main differences in their construction lies behind whether the combination of the lock can be changed. I will first discuss the basic design of a lock with a standard factory set combination which are much simpler in their construction and will later explain the more complex type which allows the owner of the lock to change the combination, as on brief cases for example.
Both type of locks will consist of a number of discs which will be numbered on their outer edge. However, with the lock which cannot have its combination changed there will be a notch on the inside directly behind one of the numbers of each disc. It is when these notches are in line that part of the lock will be allowed to move, thus opening the lock. On the bicycle chains above for example, one end of the chain consists of the locking part and the other will be a plug with a number of small pegs on its edge. The pegs will be just large enough to move through the notches of the discs.
When the lock is locked the plug will be in place which will position these pegs behind each disc and will be prevented from moving due to the solid part of the discs. However, when the discs are in their correct order the notches will be positioned where the pegs are and thus allow the plug to be removed.
The same principle of the bicycle lock lies behind locks which may instead have a shackle instead of a plug as is the case with other types of bicycle locks and padlocks. The diagram below shows a different type of bicycle chain, this time with a shackle, and also a padlock.
The difference between the simple bicycle lock explained above and the locks with shackles is simply that it is a section of the shackle which has the pegs on which allows the shackle to lock instead of a plug.
Combination disc locks which can be changed are constructed in a slightly different way, and this is that it is not the disc itself which has the notch removed but is instead a separate part of the mechanism.
The diagram below shows the internal workings of a brief case lock with these separate parts labelled.
These separate parts of the lock are usually smaller plastic discs which instead of having a notch removed on its interior have a point removed on its exterior, (see above).
The case locks due to a small grid which is part of the bolt and attached to the button which is pushed outwards to open the lock. It is this grid which fits around the metal and also the plastic discs and locks the case as the plastic discs will protrude through each section of the grid.
When the correct combination has been entered the metal numbered discs will inturn rotate the plastic discs to the point at which a part has been removed. Therefore the plastic discs will no longer protrude through this grid and will allow the grid and bolt to move opening the case.
In order to change the combination of a brief case lock a small switch is moved on the inside of the case. This has the effect of moving a small rod and with it these plastic discs. Therefore, if the numbered discs are now rotated they will not interfere with the plastic discs which will remain in the same position allowing a new combination to be chosen. When the switch on the inside of the case is again moved the rod will slide back and the plastic discs will enter the numbered discs, this time with the point allowing the grid to open where the numbers of the new combination are.
Push Button Combination Padlock
This type of combination lock is shown in the diagram below.
When the correct numbered buttons are depressed the switch on the base of the lock will be able to move and the shackle will snap open.
This type of lock consists of a grid which when moved will open the lock. Notches cut from the buttons will allow this grid to move and therefore, the lock to open
It is where these notches are located on each button which decides on the combination of the lock.
The numbers which do not form part of the lock will have notches which will already be in line with the grid, however the notches on the buttons forming the combination will only be in line when they are depressed therefore allowing the lock to open.
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