Gas leak detector for detecting a leak of gas from - a first type of leak of gas from a gas container valve unit and/or - a second type of leak of gas between the gas container valve unit and the gas container and/or - a third type of leak of gas through a wall or a welding of the gas container, the gas-leak detector comprises - a housing (106a, 106b) which can be moved relatively to an external surface (107, 109) so as at least partly to surround the gas container valve unit, where the housing comprises means for providing a substantially closed connection between the housing and the external surface when the housing is moved relatively to the external surface in order to form a substantially closed space within the housing, wherein the substantially closed space is a space where a gas may possibly be forced into, but where any gas is substantially not allowed to or able to exit, and - detection means (132, 130) for detecting the first and/or the second and/or the third leak of gas and configured so that the detection is provided in the substantially closed space in the housing while any leak of gas remains within the substantially closed space, and wherein the gas leak detector further comprises - an air flow generator, such as a single fan, for providing and moving a mixture of air and any leak of gas within the substantially closed space. - a first type of leak of gas from a gas container valve unit and/or - a second type of leak of gas between the gas container valve unit and the gas container and/or - a third type of leak of gas through a wall or a welding of the gas container, the gas-leak detector comprises - a housing (106a, 106b) which can be moved relatively to an external surface (107, 109) so as at least partly to surround the gas container valve unit, where the housing comprises means for providing a substantially closed connection between the housing and the external surface when the housing is moved relatively to the external surface in order to form a substantially closed space within the housing, wherein the substantially closed space is a space where a gas may possibly be forced into, but where any gas is substantially not allowed to or able to exit, and - detection means (132, 130) for detecting the first and/or the second and/or the third leak of gas and configured so that the detection is provided in the substantially closed space in the housing while any leak of gas remains within the substantially closed space, and wherein the gas leak detector further comprises - an air flow generator, such as a single fan, for providing and moving a mixture of air and any leak of gas within the substantially closed space. the gas-leak detector comprises - a housing (106a, 106b) which can be moved relatively to an external surface (107, 109) so as at least partly to surround the gas container valve unit, where the housing comprises means for providing a substantially closed connection between the housing and the external surface when the housing is moved relatively to the external surface in order to form a substantially closed space within the housing, wherein the substantially closed space is a space where a gas may possibly be forced into, but where any gas is substantially not allowed to or able to exit, and - detection means (132, 130) for detecting the first and/or the second and/or the third leak of gas and configured so that the detection is provided in the substantially closed space in the housing while any leak of gas remains within the substantially closed space, and - a housing (106a, 106b) which can be moved relatively to an external surface (107, 109) so as at least partly to surround the gas container valve unit, where the housing comprises means for providing a substantially closed connection between the housing and the external surface when the housing is moved relatively to the external surface in order to form a substantially closed space within the housing, wherein the substantially closed space is a space where a gas may possibly be forced into, but where any gas is substantially not allowed to or able to exit, and - detection means (132, 130) for detecting the first and/or the second and/or the third leak of gas and configured so that the detection is provided in the substantially closed space in the housing while any leak of gas remains within the substantially closed space, and wherein the gas leak detector further comprises - an air flow generator, such as a single fan, for providing and moving a mixture of air and any leak of gas within the substantially closed space. - an air flow generator, such as a single fan, for providing and moving a mixture of air and any leak of gas within the substantially closed space.