Abstract: Method and device for indicating movements of gas bubbles in a liquid, droplets of liquid in a gas or a level of liquid, the liquid or the gas forming a medium in a conduit (15) or a container. Microwave signals of a predetermined frequency are transmitted through a section (G) of the conduit (15) or the container (16) that is pervious to microwaves toward said medium, and microwave signals reflected from the medium are received. Received microwave signals are then utilized to indicate presence of gas bubbles, droplets, or a level of a liquid moving in said conduit (15) or said container (16).Said conduit (15) is designed with a section (G) that is pervious to microwaves, and a microwave transmitter (S) is provided to transmit microwave signals towards said section (G). A microwave receiver (M) is provided to receive microwave signals that are reflected from the medium, and said microwave receiver (M) is operatively connected to a detector (6).