A connecting device for connecting a gas sensor to a gas leak detector, wherein the gas sensor comprises an elongate sensor housing having two opposite frontal ends and the gas leak detector comprises at least one first gas connector adapted to be connected to the gas sensor, characterized by a guide rail connected to the gas leak detector, said guide rail engaging with the sensor housing such that, in an end position of the gas sensor, the at least one first gas connector engages with at least one complementary second gas connector of the gas sensor in a gas-conducting manner, a fastening claw comprising two elastic spring legs extending in parallel to each other and arranged at one of the sensor housing and the gas leak detector, wherein each one of the two spring legs comprises a latching boss engaging the frontal end of the gas sensor opposite the second gas connector for retaining it in its distal end position and preventing a displacement in the proximal direction, and a spreading element having two retaining arms configured for gripping around the frontal end of the sensor housing, wherein each retaining arm comprises a pulling edge for gripping behind the frontal end, and wherein each retaining arm comprises an inclined insertion portion along which the latching boss of a spring leg grips and pivots the spring leg against the spring force when the spreading element is displaced in the distal direction, and wherein each retaining arm comprises an inclined disengagement portion where in the distal end position of the sensor housing, when the pulling edges engage with the frontal end of the sensor housing, the latching bosses engage the inclined disengagement portions and increase a mechanical resistance which is to be overcome for displacing the sensor housing and the spreading element in the proximal direction along the guide rail. a guide rail connected to the gas leak detector, said guide rail engaging with the sensor housing such that, in an end position of the gas sensor, the at least one first gas connector engages with at least one complementary second gas connector of the gas sensor in a gas-conducting manner, a fastening claw comprising two elastic spring legs extending in parallel to each other and arranged at one of the sensor housing and the gas leak detector, wherein each one of the two spring legs comprises a latching boss engaging the frontal end of the gas sensor opposite the second gas connector for retaining it in its distal end position and preventing a displacement in the proximal direction, and a spreading element having two retaining arms configured for gripping around the frontal end of the sensor housing, wherein each retaining arm comprises a pulling edge for gripping behind the frontal end, and wherein each retaining arm comprises an inclined insertion portion along which the latching boss of a spring leg grips and pivots the spring leg against the spring force when the spreading element is displaced in the distal direction, and wherein each retaining arm comprises an inclined disengagement portion where in the distal end position of the sensor housing, when the pulling edges engage with the frontal end of the sensor housing, the latching bosses engage the inclined disengagement portions and increase a mechanical resistance which is to be overcome for displacing the sensor housing and the spreading element in the proximal direction along the guide rail.