Abstract: An apena monitor detects breathing movement by a strap attached around the thorax region of the patient together with a Hall effect detector which is arranged to detect expansion movements of the body of the patient. The detector includes a first part mounted on one part of the strap and a transducer element attached to a second part of the strap so as to be pulled away from the first part against the bias of a spring and released toward the first part in dependence upon the movement. The position of the transducer element relative to the first part is transmitted wirelessly to a receiver using an antenna mounted on the bed frame construction. The signals are decoded to produce a series of values each dependent upon an instantaneous position of the transducer element. The values are monitored to detect increasing and decreasing values indicative of an aperiodic sinusoidal pattern associated with breathing.