Elderly and patients with abnormalities in the control of body movement need automatic alarm with privacy protection when they fall. this paper proposes octagonal formation of ultrasonic array sensors for fall detection system in a smart room. In the method, octagonal array is designed to install ultrasonic sensors on a wall and roof. Signals of ultrasonic reflected from object in the room are processed to recognize fall. In experiments, the proposed method is proved 94% accuracy in fall detection.