A safety sensor (1) for detecting excessive levels of liquid, arriving preferably from a respective conveyance channel (4), in a humidification chamber (2) of assisted respiration units. The sensor (1) comprises a float (8), which is adapted to stay on the free surface of the liquid contained in the chamber (2) and is provided with an element (9) that can slide on a guide (10), the sliding being determined by the thrust applied by the liquid on the float (8). Along the guide (10) there is a signal circuit (11), which can comprise the guide (10), the value in output from the signal circuit (11) being defined by the length of the portion of the element (9) that is present on the guide (10).
