The invention relates to a safety device and a securing method, in particular for securing firearms against unauthorised use. A device according to the invention is provided with at least one clamping or locking portion that is insertable into a barrel 100 of a firearm and is optionally lockable and/or unlockable or permanently clampable therein and/or detachable therefrom. Moreover, it is provided with a control unit, such as an electronic authentication means that is capable of authenticating a user and, if the user is authorized, makes at least one clamping portion clampable within the barrel of the weapon or detachable therefrom. The safety device is completely insertable into the barrel.
