The present invention relates to a method and to a device for detecting the entry of air in a fluid system, in particular in an extracorporeal blood circuit of a blood treatment device comprising an arterial branch leading to the blood treatment unit and a venous branch leading from said blood treatment unit. The method has a binary data conversion step which receives a mark-up language document written in a mark-up language and converts the mark-up language document to binary data composed of commands and data that can be processed by the device. The system 1 has a connecting cable 52 connecting with both instruments 20 and 40 to carry out communication with each other. In a more specific embodiment, the UV-LED structure includes n-type metallization layer, passivation layers, and bond pads positioned at appropriate locations of the device.