Electronic Fetal Heart Monitoring can be done by listening to your baby's heartbeat with a special stethoscope. More often, it is done using two flat devices (sensors). They are held in place with elastic belts on your belly. One sensor uses reflected sound waves (ultrasound) to keep track of your baby's heart rate. The other sensor measures how long your contractions last. The sensors are connected to a machine that records the details . can the phone be used for recording this signal?