The BT-300 Acoustic Simulator an accessory made for the BT-300 Fetal Monitor. In the non stress test, you will place a heart-rate monitor on the abdomen wall to see how the fetus's heart rate changes when he/she moves. If he/she is asleep, if you press the fetal acoustic stimulation device on the abdomen wall it provides a sound wave to wake him/her up, so he/she starts moving again.