A device implantable in a living body, subcutaneously, and adapted to emit and/or receive data to or from the outside of the body and to receive energy by electromagnetic coupling with a coil of an external device, said implantable device including for that purpose at least one coil, a tight case containing electronic means at least for stimulation and/or collection, a magnet adapted to hold and centre the coil of said external device with said at least one coil of the implantable device, characterized in that: - said case includes: • a hollow crown (16 1) made of a biocompatible and electromagnetic wave permeable material, including: ▪ an external wall forming the radial periphery of the case, and ▪ an internal wall (11 i) oriented towards the centre of the tight case and forming a central housing in the middle of the tight case, ▪ the external wall and the internal wall (11 i) forming the opening of a U-shaped annular groove, • a bottom made of a biocompatible material tightly closing the opening of the hollow part (16 2) of the crown (16 1), and • the hollow part (16 2) of the crown (16 1) containing at least the electronic means and said at least one coil, - said magnet has a size compatible with the central housing formed by the internal wall (11 i) of the crown (16 1) and is placed in said central housing in the middle of the tight case in a reversible and extractible manner. - said case includes: • a hollow crown (16 1) made of a biocompatible and electromagnetic wave permeable material, including: ▪ an external wall forming the radial periphery of the case, and ▪ an internal wall (11 i) oriented towards the centre of the tight case and forming a central housing in the middle of the tight case, ▪ the external wall and the internal wall (11 i) forming the opening of a U-shaped annular groove, • a bottom made of a biocompatible material tightly closing the opening of the hollow part (16 2) of the crown (16 1), and • the hollow part (16 2) of the crown (16 1) containing at least the electronic means and said at least one coil, - said magnet has a size compatible with the central housing formed by the internal wall (11 i) of the crown (16 1) and is placed in said central housing in the middle of the tight case in a reversible and extractible manner. • a hollow crown (16 1) made of a biocompatible and electromagnetic wave permeable material, including: ▪ an external wall forming the radial periphery of the case, and ▪ an internal wall (11 i) oriented towards the centre of the tight case and forming a central housing in the middle of the tight case, ▪ the external wall and the internal wall (11 i) forming the opening of a U-shaped annular groove, ▪ an external wall forming the radial periphery of the case, and ▪ an internal wall (11 i) oriented towards the centre of the tight case and forming a central housing in the middle of the tight case, ▪ the external wall and the internal wall (11 i) forming the opening of a U-shaped annular groove, • a bottom made of a biocompatible material tightly closing the opening of the hollow part (16 2) of the crown (16 1), and • the hollow part (16 2) of the crown (16 1) containing at least the electronic means and said at least one coil, - said magnet has a size compatible with the central housing formed by the internal wall (11 i) of the crown (16 1) and is placed in said central housing in the middle of the tight case in a reversible and extractible manner. - said magnet has a size compatible with the central housing formed by the internal wall (11 i) of the crown (16 1) and is placed in said central housing in the middle of the tight case in a reversible and extractible manner.