This biofeedback device provides relief for stress in as little as 15 minutes without the use of medication by teaching you to synchronize your breathing with the activity of your nervous system activity for optimal physical and mental relaxation. Relaxation occurs when your vagus nerve (the nerve responsible for decreasing heart rate and pacifying organs) activates, and breathing exercises--like those used in yoga and tai chi--can induce this state when inhaling and exhaling coincide with the activity of the vagus nerve. After determining your pulse, a wavelength that represents your vagus nerve is shown on the easy-to-read LCD, and the unit provides visual and audible cues that help you synchronize your breathing with the peaks of the wavelength, resulting in optimal vagus nerve activity and relaxation. About the size of an MP3 player, the unit stores unobtrusively in a pocket for convenient travel. Includes two AAA batteries 3 3/4" L x 2 1/2" W x 3/4" D. (8 oz.)