A house key is the most common sort of key. There are two main forms. The older form is for lever locks, where a pack of flat levers (typically between two and five) are raised to different heights by the key whereupon the slots or gates of the levers line up and permit a bolt to move back and forth, opening or closing the lock. The teeth or bittings of the key have flat tops rather than being pointed. Lever lock keys tend to be bigger and less convenient for carrying, although lever locks tend to be more secure.
The more recent form of house key is that for a pin-tumbler or wafer-tumbler lock. When held upright, as if to open a door, a series of grooves on either side of the key (the key´s blade) limits the type of lock the key can slide into. As the key slides into the lock, the grooves on the blade of the key align with the wards in the keyway allowing or denying entry to the cylinder. Then a series of pointed teeth and notches on the blade called bittings allow pins or wafers to move up and down until they align with the shear line of the inner and outer cylinder, allowing the cylinder or cam to rotate freely inside the lock, which opens the lock. 
Car ignition and steering wheel lockMain article: Power door locks
A car key or an automobile key is a key used to open and start an automobile, or both. Modern key designs are usually symmetrical, and some use grooves on both sides, rather than a cut edge, to actuate the lock. It has multiple uses for the automobile with which it was sold. A car key can open the doors, as well as start the ignition, open the glove compartment and also open the trunk (boot) of the car. Some cars come with an additional key known as a valet key that starts the ignition and opens the driver´s side door, but prevents the valet from gaining access to valuables that are located in the trunk or the glove box. Some valet keys, particularly those to high-performance vehicles, go so far as to restrict the engine´s power output to prevent joyriding. Recently, features such as coded immobilizers have been implemented in newer vehicles. More sophisticated systems make ignition dependent on electronic devices, rather than the mechanical keyswitch.
Ignition switches or locks are combined with security locking of the steering column (in many modern vehicles) or the gear lever (such as in Saab Automobile vehicles). In the latter, the switch is between the seats, preventing damage to the driver´s knee in the event of a collision.
Keyless entry systems, which use either a door-mounted keypad or a remote control in place of a car key, are becoming a standard feature on many new cars. Some of them are handsfree.
Some high-tech automotive keys are billed as theft deterrents. Mercedes-Benz uses a key that, rather than have a cut metal piece to start the car, uses an encoded infrared beam that communicates with the car´s computer. If the codes match, the car can be started. These keys can be expensive to replace if lost and can cost up to US $400.
A switchblade key is basically the same as any other car key, except in appearance. The switchblade key is designed to fold away inside the fob when it is not being used. Switchblade keys have become very popular recently because of their smart compact look. This type of key has also been known to be confiscated by airport security officials.
Because switchblade keys are only developed for new car models, they are usually equipped with a programmed transponder chip.
A master key operates a set of several locks. Usually, there is nothing special about the key itself, but rather the locks into which it will fit. These locks also have keys that are specific to each one (the change key) and cannot operate any of the others in the set. Locks that have master keys have a second set of the mechanism used to operate them that is identical to all of the others in the set of locks. For example, master keyed pin tumbler locks will have two shear points at each pin position, one for the change key and one for the master key. A far more secure (and more expensive) system has two cylinders in each lock, one for the change key and one for the master key.
Larger organizations, with more complex "grandmaster key" systems, may have several masterkey systems where the top level grandmaster key works in all of the locks in the system.
A practical attack exists to create a working master key for an entire system given only access to a single master-keyed lock, its associated change key, a supply of appropriate key blanks, and the ability to cut new keys. This is described in Cryptology and Physical Security: Rights Amplification in Master-Keyed Mechanical Locks. Master keyed locks are also easier to pick, due to the fact the lock has two shear points.
Locksmiths may also determine cuts for a replacement master key, when given several different key examples from a given system.
A control key is a special key used in removable core locking systems. The control key enables a user with very little skill to remove from the cylinder, quickly and easily, a core with a specific combination and replace it with a core with a different combination. In Small Format Interchangeable Cores (SFIC), similar to those developed by Frank Best of the Best Lock Corporation, the key operates a separate shear line, located above the operating key shear line. In Large Format Removable Cores (LFRC), the key may operate a separate shear line or the key may work like a master key along the operating shear line and also contact a separate locking pin that holds the core in the cylinder. SFIC´s are interchangeable from one brand to another, while LFRC´s are not.
Transponder keys may also be called “chip keys”. Transponder keys are automotive ignition keys with signal-emitting circuits built inside.
When the key is turned in the ignition cylinder, the car´s computer transmits a radio signal to the transponder circuit. The circuit has no battery; it is energized by the radio signal itself. The circuit typically has a computer chip that is programmed to respond by sending a coded signal back to the car´s computer. If the circuit does not respond or if the code is incorrect, the engine will not start. Many cars immobilize if the wrong key is used by intruders. Chip Keys successfully protect cars from theft in two ways: forcing the ignition cylinder won´t start the car, and the keys are difficult to duplicate. This is why chip keys are popular in modern cars and help decrease car theft.
Many people who have transponder keys are not aware of the fact because the circuit is hidden inside the plastic head of the key. On the other hand, General Motors produced what are known as VATS keys (Vehicle Anti-Theft System) during the 1990s, which are often erroneously believed to be transponders but actually use a simple resistor, which is visible in the blade of the key. If the value of the resistor is wrong, or the key is a normal key without a resistor, the circuit of the car´s electrical system will not allow the engine to be started.
SentrySafe four-sided keyA double-sided key is very similar to a house or car key with the exception that it has two sets of teeth, an upper level standard set of teeth and a lower, less defined set of teeth beside it. This makes the double-sided key´s profile and its corresponding lock look very similar to a standard key while making the attempt to pick the lock more difficult.
Four-sided keyA four-sided key (also known as a cross or cruciform key) has four sides, making it not only harder to duplicate and the lock harder to pick but also more physically durable.
Paracentric keyA paracentric key is designed to open a paracentric lock. It is distinguishable by the contorted shape of its blade, which protrudes past the centre vertical line of the key barrel. Instead of the wards on the outer face of the lock simply protruding into the shape of the key along the spine, the wards protrude into the shape of the key along the entire width of the key, including along the length of the teeth.
Internal cut keyAn internal cut (also known as "Sidewinder" or "Laser Cut") key has a rectangular blade with a wavy groove cut up the center of the face of blade, at constant depth.
Typically the key has an identical wavy groove on the back of the blade, making it symmetrical so it works no matter which way it is inserted. Also referred to as the inner profile or sidewinder. These keys must be cut by special key cutting machines made for them. 
Abloy keyMain article: disc tumbler lock
Abloy keys are cut from a metal half-cylinder. The cuts are made at different angles, so when the key is turned in the lock it rotates each disk a different amount.
A dimple key has a rectangular blade with various cone-shaped dimples drilled into the face of the blade at various depths. Typically the lock has 2 rows of pins that match up with 2 rows of dimples. Typically the key has the same dimple pattern on the back of the blade, making it symmetrical so it works no matter which way it is inserted.[10