An array of acoustic sensors that can be worn around the neck to pick up breathing patterns and heartbeat rates could help monitor soldiers’ physiological condition on the battlefield. The prototype sensors, under development at the U.S. Army Research Laboratory, consist of microphones embedded in gel-filled pads. The gel, whose density and sound speed match those of human tissue, optimizes the conduction of sound from within the skin to the sensor. It also blocks out ambient noise (likely to be very loud on a battlefield). By listening to the sound of blood flow and respiration, the sensor monitors heart and breath rates, blood pressure, coughing, vomiting and other symptoms of distress. The sensors would transmit their readings to a remote receiver via a wireless communications device. The sensors can also be worn on the wrist or a headband (photo), making them less cumbersome than vests that are also under development for similar monitoring applications. The sensors remain several years from battlefield readiness.