See this video from RCC Nursing Professor Ms. Miller to learn about the TENS unit!
The sensor you make here measures voltages from your skin. The TENS unit sends voltage to your body instead, it's like the opposite thing.
Building the finger sensors.
You need a good conductive connection for the finger sensors. The "sensor" is literally aluminum foil connected to a jumper wire and then wrapped around your finger. You can use Velcro or tape to fix it around your finger.