A trigger lock is a device designed to prevent a firearm from being discharged while the device is in place. Generally, two pieces come together from either side behind the trigger and are locked in place, which can be unlocked with a key or combination. This physically prevents the trigger from being pulled to discharge the weapon. Other types of trigger locks do not go behind the trigger, but encompass the full area behind the trigger guard making the trigger inaccessible.
There is controversy surrounding manufacturing standards, usage, and legislation of trigger locks. While supporters of trigger locks argue that they will save children from dying in gun accidents, critics point to demonstrations that some models can be removed by children with very little force and common household tools. Many firearms can go off if the gun is dropped. It is important to make sure to look for firearms that fully disengage the hammer when the safety is put on.A spokesperson for Master Lock, a trigger lock manufacturer, was quoted as saying “If you put a trigger lock on any loaded gun, you are making the gun more dangerous.”Critics also point out that a trigger lock will increase the time it takes a gun owner to respond to a self-defense emergency. In 2008, the U.S. Supreme Court overturned a Washington, D.C. law that required handguns to be locked or otherwise kept inoperative within the home, saying that this "makes it impossible for citizens to use them for the core lawful purpose of self-defense."
Although there are no universal standards for the design or testing of trigger locks, some jurisdictions, such as the state of California, maintain a list of approved trigger lock devices.In Canada, a trigger lock is one of the methods prescribed by law to secure a firearm during transport or storage.