Abstract: A housing of U-shaped cross section fits over the trigger guard of a gun to cover the trigger guard and prevent access to the trigger. A latch member is disposed in the housing and is biased by an elastic member, for example, a spring, to engage the trigger guard. An external member is accessible from the outside of the housing for manual pressing to overcome the spring and thereby depress the latch for removing the housing from the trigger guard. By selecting the strength of the spring the gun can be rendered safe against children who have not enough strength to overcome the spring. Adults, however, can quickly remove the housing by manual pressure and make the gun instantly available for use.