A removable firearm chamber-obstruction mechanism includes a locking mechanism including at portion configured to be inserted in a chamber of a firearm and engage the chamber so as to be locked in place. The locking mechanism includes one or more finger actuators, a thumb bar actuator engaged with the one or more finger actuators, a release key connected to the thumb bar actuator, and a tooth key disposed in abutment against the release key. A handle covers the locking mechanism, and a lid encloses the handle. The locking mechanism locks and unlocks the tooth key upon a successful manual actuation of the one or more finger actuators and the thumb bar actuator, such that the tooth key engages the chamber in a locked position and is unengaged from the chamber in an unlocked position.