An electronic vapor provision system is provided including: a pressure drop or air flow sensor for monitoring inhalation by a user through the electronic vapor provision system; and a control unit for detecting the start and end of inhalation based on readings from the sensor. The control unit is configured to: monitor the cumulative period of inhalation (Ti) over a predetermined window (Tw); and transfer the electronic vapor provision system to a sleep mode if the cumulative period (Ti) exceeds a predetermined threshold (Th).