Baby Sound Amplifier All parents love to hear the heartbeat of their baby. A baby sound amplifier will allow your friends to do just that. Your friends will be able to hear the heartbeat of the baby whenever they like. You also need to let your friends know that they could not hear the heartbeat during the first three months of pregnancy. The baby sound amplifier can also work as a baby monitor for you. A baby sound amplifier comes with a conductive gel that the mother needs to apply on her belly. After applying the conductive gel. she just needs to find where is her baby to hear the heartbeat of her baby.