safety interlock

In firearms, a safety or safety catch is a mechanism used to help prevent the accidental discharge of a firearm, helping to ensure safer handling.
Safeties can generally be categorized as either internal safeties (which typically do not receive input from the user) and external safeties (which the user may manipulate manually, for example, switching a lever from "safe" to "fire"). Sometimes these are called "passive" and "active" safeties (or "automatic" and "manual"), respectively. External safeties typically work by preventing the trigger from being pulled or preventing the firing pin from striking the cartridge.
Firearms which allow the user to select various fire modes may have separate controls for safety and for mode selection (e.g. Thompson submachine gun) or may have the safety integrated with the mode selector as a fire selector with positions for safe, semi-automatic, and fully automatic fire (e.g. M16 rifle).
Some firearms manufactured after the late 1990s and early 2000s include a mandatory integral locking mechanisms that must be deactivated by a unique key before the gun can be fired. These integral locking mechanisms are intended as child-safety devices during unattended storage of the firearm—not as safety mechanisms while carrying. Other devices in this category are trigger locks, bore locks, and gun safes.

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