For the first time in decades the annual number of gun-related deaths in the U.S. is expected to surpass the annual count of automobile fatalities. In 2013, the most recent year for which data are available, the two were on par: motor vehicles killed 33,804 people, and firearms killed 33,636, according to the U.S. Centers for Disease Control and Prevention. Firearm deaths and injuries have grown to pose a major public health problem, says Stephen Teret, co-director of the Johns Hopkins Center for Law and the Public's Health. Teret studies how to make safer guns for consumers. And he is not the only person doing so. The first symposium on smart guns—weapons that only specific users can fire—was held earlier this year. Several gun technologies to prevent unauthorized or accidental discharge and to stem crime have moved beyond proof of concept and into production—albeit at a limited scale.

Radio-Frequency Identification (RFID)

The most mature smart guns on the market are RFID systems equipped with a locking mechanism that releases only when a gun draws close to a device broadcasting a particular radio band. German firm Armatix introduced an RFID gun to the U.S. in 2013 that activates when a person enters a PIN on a nearby paired watch. Similarly, the company TriggerSmart Technologies sells a gun that automatically unlocks when the owner's ring, which contains an authorization tag, comes within two inches of a reader in the weapon's handle. These guns could cut down on teen suicides and accidental shootings, Teret says.

Biometrics

Biometric smart guns require proof of identity—via human body characteristics—to operate. In theory, anything from a voiceprint to a retinal scan could serve as a key, but most versions available analyze hand-related features, such as fingerprints. The company Intelligun, for example, sells a fingerprint-locking system for $399 that can be mounted on the grip of a model 1911 pistol. As soon as the owner relaxes his or her hold, the gun relocks. But gloves, dirt and blood can interfere with these readers. So engineers at the New Jersey Institute of Technology have worked with the U.S. Army Armament Research, Development and Engineering Center on a dynamic recognition technology that reads the pressure profile of the owner's clutch. Tests with a prototype of the technology on the SIG Sauer P228 (a handgun used by police departments in New Jersey and elsewhere) are ongoing.

Microstamping

A technique called microstamping imprints tiny identifying marks from a gun onto a cartridge as it fires. The resulting indentations could help law enforcement quickly link an individual weapon, and therefore a suspect, to a shooting. During manufacturing and assembly, lasers etch microscopic markings on internal parts of the gun, such as the firing pin. When the gun is fired, those imprinted parts strike the softer metal of the cartridge, transferring the markings. In 2013 experts tested the system on different types of firearms and ammunition and found that the success of transfer varied widely. The technology, however, continues to make inroads. In February a district court judge upheld the constitutionality of a 2007 California law that bans the sale of new handguns without microstamping capability. New York State is now considering a similar law.