When your Stemoscope is working, use your finger to tap/knock the diaphragm. If you can hear a loud dub sound with your earphones and high volume when you tap/knock, the Stemoscope works well. Heart sounds are easy to be detected. You may listen to your heartbeats. If you can hear your heartbeats clearly, your Stemoscope works well. Please don’t forget to wear your earphones and increase your phone volume if necessary.