A control-free ventilator alarm.

An alarm for use with positive-pressure lung ventilators is described. The device gives audible warning if the pressure in the patient circuit fails either to exceed or to fall below 15 cmH2O within a period of 20 seconds or if the batteries are running low. No external controls are provided and the alarm is activated when a probe connected to the breathing circuit is inserted into the alarm. The probe whistles if incorrectly connected during intermittent positive pressure ventilation. Battery life in clinical practice is longer than 6 months.