A method and a system (400) for detection and position determination of chips (100), which transmit ultrasound signals in a room. The system (400) comprises electronic identification chips (100), which are attached to objects that have to be monitored. Each chip (100) is equipped with a transmitter (179) and a receiver (180). The signals are received by a plurality of detector units (290), which are connected to a detector base unit (200) that registers and interprets the signals transmitted form the identification chips (100). Detector base units (200) located in different rooms are interconnected in a network (215) and transmit processed information to one or more central units (410) for further interpretation and sorting. The special feature of the invention is that line interference is substantially removed, and it is possible to determine position even though the identification chips (100) are in motion.