Wellstarter AS has developed a patented downhole flow monitoring solution based on heat pulses released into the well stream. The system comprises autonomous heat source(s), and software for interpretation of resulting heat pulses. The heat source requires no cabling, does not release any material, and one or more sources can be installed along the productive zones of the well. The heat pulse is picked up by an existing downhole pressure/temperature gauge (PDG), and can be analysed real-time, onsite or remotely.