Step 18: Headphones
Put on the headphones. Notice how you can adjust the length of the beep by tensing and relaxing your muscle.
Now, you can train yourself to produce a sound of a certain duration by concentrating on that muscle group.
You can also monitor the sensor readings by plugging the Arduino back into the computer and turning on the serial monitor. Make certain you unplug any external voltage sources to the Arduino before you try this.