Apparatus designed for the transmission of signals using electromagnetic waves of a certain wavelength (λ) from a housing which is at least partially metallic and designed for use in a hazardous area, comprising: - the housing with a defined wall thickness (D Gehäuse), wherein the housing essentially has a rotationally symmetrical, preferably cylindrical, outer contour, - a transmission/reception unit arranged in the housing, wherein said unit is designed to generate and/or receive electromagnetic waves, - at least a primary antenna arranged in the housing, wherein said antenna is designed to couple and/or decouple electromagnetic waves, and to transmit the electromagnetic waves to the transmission/reception unit, - at least one slot-like housing opening, which is designed in such a way that - with the interaction of the primary antenna - the signals are transmitted into and out of the housing with the help of the electromagnetic waves, characterized in that - a molded piece (23, 231, 232, 233, 234, 235, 236) made from a material that has a relative dielectric constant truly greater than one, wherein said molded piece has a slot-shaped section - which projects out and is adapted to the slot-shaped housing opening - with which the molded piece engages at a maximum in the housing opening down to a specific depth (T Leiter), wherein the specific depth (T Leiter) is selected in such a way that a sphere or semi-sphere with a given diameter does not touch the molded piece when placed on the at least one slot-shaped housing opening, wherein the molded piece further has a section that surrounds the slot-shaped section and is adjacent to the slot-shaped section, with a minimum width (B Leiter), wherein the molded piece with the circumferential area is pressed against an inner side of the housing in the area around the at least one slot-shaped housing opening and the minimum width of the circumferential area is designed in such a way that it produces a shortest path - for a gas according to standard IEC 60079, edition of 27 June 2014 - through the at least one slot-shaped housing opening from the interior to the exterior of the metallic housing, said path being at least 3 mm if V ≤ 10 cm 3 applies for the volume, or of at least 6 mm if 10 cm 3 < V ≤ 100 cm 3 applies for the volume, or at least 10 mm if V > 100 cm 3 applies for the volume, wherein the free space enclosed by the entire housing is defined as the volume V. - the housing with a defined wall thickness (D Gehäuse), wherein the housing essentially has a rotationally symmetrical, preferably cylindrical, outer contour, - a transmission/reception unit arranged in the housing, wherein said unit is designed to generate and/or receive electromagnetic waves, - at least a primary antenna arranged in the housing, wherein said antenna is designed to couple and/or decouple electromagnetic waves, and to transmit the electromagnetic waves to the transmission/reception unit, - at least one slot-like housing opening, which is designed in such a way that - with the interaction of the primary antenna - the signals are transmitted into and out of the housing with the help of the electromagnetic waves, - a molded piece (23, 231, 232, 233, 234, 235, 236) made from a material that has a relative dielectric constant truly greater than one, wherein said molded piece has a slot-shaped section - which projects out and is adapted to the slot-shaped housing opening - with which the molded piece engages at a maximum in the housing opening down to a specific depth (T Leiter), wherein the specific depth (T Leiter) is selected in such a way that a sphere or semi-sphere with a given diameter does not touch the molded piece when placed on the at least one slot-shaped housing opening, wherein the molded piece further has a section that surrounds the slot-shaped section and is adjacent to the slot-shaped section, with a minimum width (B Leiter), wherein the molded piece with the circumferential area is pressed against an inner side of the housing in the area around the at least one slot-shaped housing opening and the minimum width of the circumferential area is designed in such a way that it produces a shortest path - for a gas according to standard IEC 60079, edition of 27 June 2014 - through the at least one slot-shaped housing opening from the interior to the exterior of the metallic housing, said path being at least 3 mm if V ≤ 10 cm 3 applies for the volume, or of at least 6 mm if 10 cm 3 < V ≤ 100 cm 3 applies for the volume, or at least 10 mm if V > 100 cm 3 applies for the volume, wherein the free space enclosed by the entire housing is defined as the volume V.