A safe is provided for use with a wall having an air duct and an opening to the wall which connects the air duct with a room. The safe includes a housing having an interior dimensioned to fit within the air duct so that the housing is recessed in the wall and in alignment with the wall opening. A grille dimensioned to cover the wall opening is pivotally mounted to the housing so that the grille is movable between a closed position in which the grille overlies and covers the wall opening and an open position in which the opening interior is accessible from the room. A valuable container is mounted within the housing or, alternatively, on the rear side of the grille. Additionally, air passage holes are formed through the housing for enabling air flow through the housing, grille and air duct. Alternatively, the grille is magnetically attached to the housing.