Abstract: The invention is directed to an apparatus (concealed safety device) and method for preventing unauthorized or inadvertent discharge of a firearm. The apparatus includes a plurality of annular pistons which are manipulated using a spring and hydraulic assembly. The pistons are attached to a annular engaging ring which works to obstruct the mainspring rod of a firearm when the apparatus is inserted into the associated firearm aperture. In operation, a quick manual pressure or strike to the right side of the gun handle through a concealed, thin-skinned, flexible wall allows for manual deactivation of the lock. When in the correct position the engaging ring blocks movement of the mainspring rod preventing the firearm's trigger from being pulled. The device is capable of installation at the time of manufacture or as an after-market accessory replacing the stock firearm grips.