Height adjustable beds involve the risk for the patient to fall out of the bed. In order to prevent this to happen, the bed is furnished with a device which observes whether a nursing person is within a proximity zone of the bed. When the nursing person leaves the proximity zone and the bed is adjusted to a height implying potential danger for the person in the bed, a message (sms) is sent to a mobile unit carried by the nursing person. The indication warns the nursing person, making it possible for him to prevent the potential dangerous situation by height adjustment of the bed to a safe height for leaving the bed. Hereby personal injury is prevented or minimized as much as possible.