Safety devices for use with a handheld firearm are disclosed. The safety devices include a lever that can be pivoted into the travel path of the hammer of the firearm to preclude the hammer from striking a firing pin. In an example, the lever is connected to the trigger such that the safety device is released when the trigger is pulled. In another example, the lever protrudes into the magazine shaft of the firearm such that the safety device is only released when a magazine is inserted into the shaft.