A method and a device are provided for detecting the respiratory activity of a person and for controlling the time progression of breathing gas pressure, especially in accordance with physical parameters and considering parameters indicating the momentary physiological condition of the breathing person. The device for detecting the respiratory activity of a person has at least one sensor that provides a first signal indicating the breathing gas flow, wherein at least one signal processing device is provided for processing the first signal. The signal processing device is configured in such a way that said device determines a reference-relation on the basis of the first signal detected during a first time interval. On the basis thereof, the device determines a correlation-relation between the reference-relation and the first signal. The device generates an output signal indicating the respiratory activity and/or the physiological condition of the breathing person by considering at least the correlation-relation.