A loaded chamber indicator (Figure 2, A; Figure 7) is a small device found on some pistols that displays a warning when the chamber contains a cartridge. These were first developed for use in the early 1900s by European handgun man ufacturers. Often the chamber indicator is a small pin that is built into the mechanism of the pistol. When a cartridge is in the chamber, and the action is closed, the pin protrudes from the top, back, or side of the gun.

Loaded chamber indicators have the potential to reduce unintended discharges when the user is unaware that a pistol is loaded. The user, however, must be aware that the pistol has the indicator, be able to recognize it when displayed, and respond appropriately to the information. While the device acts passively, its effectiveness may be limited by the human response. The effectiveness of this response is limited by the small size of the indicator, the potential for damage to the indi cator, and the user's level of handgun education. Loaded chamber indicators do not prevent the unauthorized use of the handgun. These devices are not found on revolvers and are found only on a limited number of pistol models. At the present time, no ind ustry standard regulates the design or availability of loaded chamber indicators on handguns.

Located on the side of the handgun (Figure 2, B; Figure 8), manual thumb safeties are intended to reduce the unintentional discharge of the weapon during normal use. Generally found only on pistols, these safeties can operate in se veral ways. Depending on the design, engagement of the safety mechanism may lock the slide, move the firing pin out of reach of the hammer, insert a block between the hammer and firing pin, or lock the hammer. In the locked position, all manual thumb sa feties, if functioning properly, prevent the handgun from discharging when the trigger is pulled. There is no industry standard for thumb safety design. Nonetheless, virtually all pistols produced have some type of manual thumb safety. Double action-on ly pistols and revolvers do not usually include this device.

A manual thumb safety is easy to use in the context of normal handgun operation, requiring only a single digit to operate. However, these safeties are active devices, requiring the user to engage the mechanism. A manual thumb safety c an be easily disengaged by children and adolescents or unintentionally disengaged by the user. Its effectiveness in preventing the unauthorized use of the handgun or an unintended discharge is limited.

Grip safeties (Figure 1, A: Figure 2, C; Figure 8 above) were originally designed in the 1880s. To discharge a handgun equipped with a grip safety, the safety lever, located on the front or back of the grip, must be compressed. Wh en holding the handgun in a normal shooting position, the safety lever is compressed by the fingers or palm (depending on the design) of the shooter’s hand, unlocking the trigger. If the shooter releases the lever, the locking mechanism automatically ree ngages. One of the most popular handgun designs containing a grip safety was the Colt 1911A (Figure 4). This gun design was the standard pistol used by the U.S. Army through much of the 20^th century.

Grip safeties are passive devices and do not hinder the use of the handgun by adults. When the gun is not being held by the grip, the grip safety reduces the risk of unintended discharge.

Grip safeties have been promoted as a means of childproofing handguns. In theory, children do not have the strength, coordination, or hand size to compress the safety lever and pull the trigger at the same time. For young children wit h small, weak hands, this theory may be accurate. With the use of two hands, however, some children may be able to discharge a handgun with a grip safety. For adolescents, a grip safety does not limit the use of the handgun.

A magazine disconnector (Figure 2, D) is a passive mechanical locking device that is designed to prevent the unintended discharge of the weapon when the magazine is removed from the pistol. Like the loaded chamber indicator, the ma gazine disconnector was originally developed in the early 1900s by European gun manufacturers. When a magazine is not fully inserted into the gun, the linkage between the trigger and the hammer release is disconnected. This prevents the pistol from bein g fired, even if a cartridge is in the chamber.

If a pistol is always handled with the magazine removed until the user is ready to shoot, then a magazine disconnector may reduce the risk of unintended discharge. However, the magazine disconnector may increase the risk of unintended discharge if the user is not familiar with its operation. An inexperienced user may insert an empty magazine into the pistol, disengaging the safety, and mistakenly assume that the gun is unloaded, even though it contains a cartridge in the chamber. For young children, storage of the gun without a magazine prevents unauthorized usage; however, older children can easily disengage the safety by reinserting the magazine. These devices are found only on a limited number of pistol models.

Drop safeties or hammer blocks (Figure 1, B; Figure 2, E; Figure 9) are designed to passively or actively prevent the unintentional discharge of the handgun if it is dropped on the hammer. On revolvers and pistols without drop safe ties or with actively engaged safeties, the hammer in the uncocked position can rest directly on the firing pin. A blow to the hammer, such as when the revolver or pistol falls out of a pocket or holster, transfers energy through the hammer to the firing pin and onto the cartridge, causing it to discharge.

Drop safeties come in a variety of designs depending on the manufacturer, with many designs having been developed for revolvers in the 1880s. In some revolver designs, a transfer bar inserts between the hammer and firing pin only when t he trigger is pulled. Without the transfer bar in place, the hammer cannot contact the firing pin.

For pistols, there are various types of firing pin blocks which act as a drop safety. This prevents the firing pin from striking the cartridge until the trigger is pulled.

Drop safety designs are generally passive, and are designed to automatically prevent unintended discharges due to dropping of the handgun. Some revolvers and pistols have active hammer blocks that prevent the hammer from striking the f iring pin, yet need to be actively engaged by the user.

Some types of handguns are manufactured with grip-mounted locks that disable the action. Some handguns are manufactured with these types of locks, or they can be added by the owner (Figure 1, C; Figure 2, F; Figure 10). Found in bo th keyed and combination styles, built-in locks prevent the handgun from being fired by someone other than the person who has access to the combination or key. The mechanisms vary depending on the type of lock. One device locks the manual thumb safety i n the engaged position, while another type internally secures the hammer. Most handguns currently available in the consumer market do not come equipped with built-in locks. After-market kits can be purchased allowing both pistol and revolver owners to r etrofit their weapons.

A built-in lock can be easy to use. When properly engaged, it limits discharge by unauthorized persons. The handgun cannot be discharged when the lock is engaged, and most locks are difficult to unknowingly disengage. Once the lock h as been disengaged, however, anyone can use the handgun.

A personalized handgun (Figure 11) is a relatively new type of handgun that prevents anyone other than an authorized user from firing the gun. These personalized handguns are modifications of standard revolvers or pistols in which a magnetic or electronic lock has been built into the grip of the gun. When the owner is not holding the handgun, the passive built-in locking device automatically secures the trigger, preventing the handgun from being fired. The owner of the personaliz ed weapon wears an identifying magnetic ring or radio transmitter bracelet. When placed next to the grip of the handgun in the proper orientation, the ring or bracelet unlocks the trigger. The grip is customized to perfectly fit the owner’s hand, allowi ng for easy alignment of the ring or bracelet.

Because a personalized handgun can discharge only when being held in the proper orientation by the owner, this system can reduce discharge by unauthorized persons such as children, adolescents and illegal owners. Personalized guns, ho wever, are not yet available in the consumer market.