An oxygen therapy monitoring device (105) comprises an oscillation chamber (403) comprised in a gas flow path (201) adapted to pass a gas flow from a source (102) to a breathing interface (106) for a person (101). The oscillation chamber induces an oscillation in the gas flow that varies as a function of a flow rate of the gas flow. A measurement arrangement (202) measures the oscillation induced in the gas flow and determines the flow rate on the basis of the oscillation that is measured.
