A fluid leak detector, comprising - detector electronics and its power supply, and - a sensor film (10, 10a) comprising - a patterned support film having round openings - a first patterned conductive electrode film formed on the top surface of the support film, a pattern of which first patterned conductive electrode film partly covers the top surface of the patterned support film - a second patterned conductive electrode film formed on the bottom surface of the patterned support film, a pattern of which second patterned conductive electrode film partly covers the bottom surface of the patterned support film, and the second patterned conductive film being configured to be placed against a surface of an application to be monitored - means configured to indicate a fluid leak when a change of resistance is measured between said patterned conductive electrode films (11, 12), characterized in that - the pattern of the first patterned conductive electrode film comprises openings, a diameter of the openings is larger than that of a drop of fluid ensued by surface tension of a fluid to be measured - the pattern of the second patterned electrode film comprises openings (1 a), a diameter of the openings is in the range of the drop of the fluid to be measured - the openings (1 a) of the second patterned conductive electrode film are aligned with the openings going through the patterned support film, and - the round openings of the first conductive electrode film and the openings (1 a) of the second patterned conductive electrode film are positioned in relation to each other such that pairs of openings on different sides of the patterned support film each have a common centre point with their pair of openings, whereby - a pattern of the patterned support film, the pattern of the first patterned conductive electrode film (1, 16a, 16b) and the pattern of the second patterned conductive electrode film (1a, 17a, 17b) are arranged in relation to each other such that a finished sensor film (10, 10a) can be cut into a shape required by the application to be monitored without a resistance value of the sensor film (10, 10a) falling below a predetermined resistance value. - detector electronics and its power supply, and - a sensor film (10, 10a) comprising - a patterned support film having round openings - a first patterned conductive electrode film formed on the top surface of the support film, a pattern of which first patterned conductive electrode film partly covers the top surface of the patterned support film - a second patterned conductive electrode film formed on the bottom surface of the patterned support film, a pattern of which second patterned conductive electrode film partly covers the bottom surface of the patterned support film, and the second patterned conductive film being configured to be placed against a surface of an application to be monitored - means configured to indicate a fluid leak when a change of resistance is measured between said patterned conductive electrode films (11, 12), - a patterned support film having round openings - a first patterned conductive electrode film formed on the top surface of the support film, a pattern of which first patterned conductive electrode film partly covers the top surface of the patterned support film - a second patterned conductive electrode film formed on the bottom surface of the patterned support film, a pattern of which second patterned conductive electrode film partly covers the bottom surface of the patterned support film, and the second patterned conductive film being configured to be placed against a surface of an application to be monitored - means configured to indicate a fluid leak when a change of resistance is measured between said patterned conductive electrode films (11, 12), - the pattern of the first patterned conductive electrode film comprises openings, a diameter of the openings is larger than that of a drop of fluid ensued by surface tension of a fluid to be measured - the pattern of the second patterned electrode film comprises openings (1 a), a diameter of the openings is in the range of the drop of the fluid to be measured - the openings (1 a) of the second patterned conductive electrode film are aligned with the openings going through the patterned support film, and - the round openings of the first conductive electrode film and the openings (1 a) of the second patterned conductive electrode film are positioned in relation to each other such that pairs of openings on different sides of the patterned support film each have a common centre point with their pair of openings, whereby - a pattern of the patterned support film, the pattern of the first patterned conductive electrode film (1, 16a, 16b) and the pattern of the second patterned conductive electrode film (1a, 17a, 17b) are arranged in relation to each other such that a finished sensor film (10, 10a) can be cut into a shape required by the application to be monitored without a resistance value of the sensor film (10, 10a) falling below a predetermined resistance value.