There are basically four types of key operated locks and two types of combination locks.
Key Operated Locks:
Warded - The simplest type of lock, the key is normally prevented from turning by means of projections in it's path, simple. Not very secure.
Disk Tumbler- A lock in which the key must move spring loaded plates to a position which will then allow a cylinder to turn, recognized by viewing the flat plated inside of the keyhole. These locks are fairly secure however they can normally be picked due to the large tolerances inside of the lock..
Lever Tumbler - These locks are one in which the key is rotated inside of the lock and causes a spring loaded plate to swing into position to allow a bar to enter a slot normally located at the end of the plate to operate the lock. These locks are considered very secure. The large "A" type of key jail locks are lever type.
Newer locks have been using rotating disks with out any springs, these are actually rotating lever tumblers, and are free to spin 360 degrees. Normally these disks are rotated into one position where a sidebar is allowed to enter a notch in the disk and allow the cylinder to rotate, these are very secure and the keys are difficult to duplicate.
Pin Tumbler-The most common type of key operated lock in the world. In these a pin, with another pin and spring is raised to the sheer line of the cylinder by the key and allows it to rotate. The pins are of varying length to allow different depths to be cut into the key and provides many combinations of different keys. Due to the closer tolerance between the two pins and the close space between the cylinder and it's hole these locks are considered secure and hard to pick.
Newer variations of these locks include having to not only raise the pin to the proper height but also rotate it to a proper position for the lock to open. Some other locks have groves machined into the side of the key to operate additional pins or other devices before the lock will open. These locks are very secure, almost impossible to pick and the keys normally can only be obtained from restricted locations, this provides for secure key control.
(OK I admit there is a fifth type, Magnetic - these locks are not very secure, are normally easily broken and fairly rare, thus I don't talk much about them.)
Combination Operated Locks:
Fixed - The combination is set at the factory and cannot be changed, normally not very secure.
Changeable - The combination can be changed by the user, not very secure
(Wheels on bottom) to Very Secure (Dial Type). There are two sub groups:
Hand Change - The combination need not be know but the lock must be
dissembled to change the combination. Many safe locks were of this type.
This also means that means the safe has to be open to change the combination!
Key Change - The lock does not need to be dissembled however the old
combination must be known to align the lock so that a change key may be
inserted and the new combination set. Most newer locks are of this type.
Now electronic locks are starting to appear. The US Government has been
using one type for protection of classified information and this lock does not
run on batteries. Spinning the dial charges up the lock and allows it to operate.
The numbers are generated on a LCD window, these are Very Secure, have
tamper devices and provide audit trails among many other features.
Lock Picking Greg Miller has a great web site on locks and lock picking. He also
has a copy of the MIT guide to lock picking on his site, and a lock pick section.
Lock Picking from How Stuff Works
Pillar Communication Locksmith information
The National Locksmith
The Locksmith Ledger
EZ change Lock Company In West Chester has a new easy change lock
Here are the codes for the VATS (Vehicle Anti Theft System)
PASS-Key Personal Automotive Security System
(Black pellet with a silver stripe on each side)
keys, by key number and resistance in Ohms:
1. 402, 2. 532, 3. 681, 4. 887, 5. 1,130, 6. 1,470, 7. 1,870, 8. 2,230,
9. 3,010, 10. 3,740, 11. 4,750, 12. 6,040, 13. 7,500, 14. 9,530, 15. 11,801.
The newer cars using keys with the large plastic heads may contain a transponder. The car looks for the factory set electronic serial number of the key (no two are alike) and will allow the car to start. Most cars can hold ten electronic serial numbers in their memory. Be well advised not to loose your last key for such a vehicle, it is difficult and costly to make such a key without one other already in the car's memory.