The inside of a typical pin tumbler lock, the first animation below shows how the pins are set to enable the cylinder to turn and release the latch/deadbolt.
You can also set pins on top of one another so that multiple keys can successfully turn the cylinder, using a "master" key and a "change" key. The idea is that several cylinders will be keyed to the "master" and each cylinder will also be keyed to its own unique "change" key.
- Cylinder Locks on Wikipedia
- Lockpicking slides and links by TOOOL (The Open Organisation of Lockpickers)
- In California, it is lawful to duplicate existent keys. Further, a "Locksmith" is defined as a person who engages "in the business of rekeying..." etc, "for any consideration or compensation whatsoever" ('consideration' meaning benefit of a contract i.e. not a gift).
(j) "Locksmith" means any person who, for any consideration or compensation whatsoever, engages, directly or indirectly and as a primary or secondary object, in the business of rekeying, installing, repairing, opening, modifying locks, or who originates keys for locks, including, but not limited to, electronic cloning of transponder keys and any other electronic programming of automotive keys and electronic operating devices, such as key fobs, door and ignition key devices, and successive electronic and other high-security key technology. A "locksmith" does not mean a person whose activities are limited to making a duplicate key from an existing key.
- In California, there are explicit exemptions for activities that would normally require a locksmith license:
- Section 6980.12 of the Business and Professions Code:
6980.12. This chapter does not apply to the following persons: (a) A person, or his or her agent or employee, who is the manufacturer of a product, other than locks and keys, and who installs, repairs, opens, or modifies locks or who makes keys for the locks of that product as a normal incident to its marketing. (b) An employee who is an industrial or institutional locksmith, provided that the employee provides locksmith services only to a single employer that does not provide locksmith services for hire to the public for any consideration or compensation whatsoever. (c) A tow truck driver who does not originate keys for locks and whose locksmith services are limited to opening motor vehicles. (d) A person employed exclusively and regularly by a state correctional institution, or other state or federal agency, and who does not provide locksmith services for hire to the public for any consideration or compensation whatsoever. (e) (1) A person registered with the bureau pursuant to Chapter 11 (commencing with Section 7500) if the duties of that person's position that constitute locksmithing are ancillary to the primary duties and functions of that person's position. (2) A person licensed, certified, or registered pursuant to Chapter 11.6 (commencing with Section 7590) if the duties of that person's position that constitute locksmithing are performed in combination with the installation, maintenance, moving, repairing, replacing, servicing, or reconfiguration of an alarm system, as defined in subdivision (n) of Section 7590.1, and limited to work on electronic locks or access control devices that are controlled by an alarm system control device, including the removal of existing hardware. (f) An agent or employee of a retail establishment that has a primary business other than providing locksmith services, providing all of the following criteria are met: (1) The services provided by the retail establishment are limited to rekeying and recombination of locks. (2) All rekeying, recombination, and installation of locks must take place on the premises of the retail establishment. (3) All rekeying, recombination, and installation services provided by the retail establishment subject to this chapter are limited to locks purchased on the retail establishment's premises and are conducted prior to purchasers taking possession of the locks. (4) An unlicensed agent or employee of the retail establishment shall not advertise or represent himself or herself to be licensed under this chapter, and an agent or employee of the retail establishment shall not advertise or represent himself or herself to be a locksmith. (5) An agent or employee of the retail establishment shall not design or implement a master key system, as defined in subdivision (o) of Section 6980. (6) An agent or employee of the retail establishment shall not rekey, change the combination of, alter, or install any automotive locks. (7) The retail establishment shall not have on its premises any locksmith tool, as defined in subdivision (s) of Section 6980, other than the following: (A) Standard key duplication machines. (B) Key blanks. (C) Pin kits. (g) A law enforcement officer employed by any city, county, city and county, state, or federal law enforcement agency, if all services are performed during the course of the officer's professional duties. (h) A firefighter or emergency medical person employed by any city, county, city and county, district, or state agency, if all services are performed during the course of duties as a firefighter or emergency medical person. (i) A new motor vehicle dealer, as defined in Section 426 of the Vehicle Code, and an employee of a new motor vehicle dealer acting within the scope of employment at a dealership.
- In California, it is lawful to possess lock picks (i.e. circumvention tools) by statue, the state must prove criminal intent.
- Burglarious And Larcenous Instruments And Deadly Weapons Section 466-469 of the California Penal Code
§ 466. Every person having upon him or her in his or her possession a picklock, crow, keybit, crowbar, screwdriver, vise grip pliers, water-pump pliers, slidehammer, slim jim, tension bar, lock pick gun, tubular lock pick, bump key, floor-safe door puller, master key, ceramic or porcelain spark plug chips or pieces, or other instrument or tool with intent feloniously to break or enter into any building, railroad car, aircraft, or vessel, trailer coach, or vehicle as defined in the Vehicle Code, or who shall knowingly make or alter, or shall attempt to make or alter, any key or other instrument named above so that the same will fit or open the lock of a building, railroad car, aircraft, vessel, trailer coach, or vehicle as defined in the Vehicle Code, without being requested to do so by some person having the right to open the same, or who shall make, alter, or repair any instrument or thing, knowing or having reason to believe that it is intended to be used in committing a misdemeanor or felony, is guilty of a misdemeanor. Any of the structures mentioned in Section 459 shall be deemed to be a building within the meaning of this section. § 466.3. (a) Whoever possesses a key, tool, instrument, explosive, or device, or a drawing, print, or mold of a key, tool, instrument, explosive, or device, designed to open, break into, tamper with, or damage a coin-operated machine as defined in subdivision (b), with intent to commit a theft from such machine, is punishable by imprisonment in the county jail for not more than one year, or by fine of not more than one thousand dollars ($1,000), or by both.