We have developed a non-intrusive safety monitoring system which can measure respiration and body movements of solitary-living elderly people while they are in their home bathroom. These physiological variables are monitored with a 40 kHz ultrasonic transmitter and four receivers. The ultrasonic transmitter diffuses an ultrasonic wave throughout the room. The diffusion pattern of this inaudible sonic energy is changed by body movements and respiration, therefore modulating the amplitude of the received ultrasonic signal. The received ultrasonic signals are demodulated by envelope detection circuits. Band-pass filters detect respirations and body movements from the envelope detection circuit outputs. These detected signals are added and used to monitor whether the elderly person is safe or not safe, while in their bathroom. When the microcomputer cannot detect body movement or respiration, it alerts the persons caregiver, via a low power personal handy phone system.