Compressed air is a widespread but costly energy carrier. Leaks account for 10 compressed air consumption in production facilities and their removal offers high potential for cost reduction. The turbulent flow from a leak causes broadband acoustic emissions. These are exploited for leak detection using a narrowband ultrasonic microphone that is insensitive to audible noise. A parabolic mirror or an acoustic horn is utilized to enhance the directivity and the received signal power of the microphone. The microphone is mounted on mobile service robots. In the project "Robotair" an automated guided vehicle (AGV) and a remotely controlled micro aerial vehicle (MAV) were used for robotized inspection of production facilities. In order to detect leaks, predefined areas are scanned. A leak is detected and localized based on the sensed peak amplitude of the ultrasound signal. The corresponding pose of the sensor facing the leak is determined based on the selflocalization of the robot. Leak localization is carried out by triangulation of two sensor poses. Tests were conducted in an automobile production facility to evaluate the performance of the system. A leak was placed in an assembly line and multiple measurements were taken from two positions with the AGV and the MAV. The leaks were successfully detected and localized.