Biometric & capacitive sensors
Touch (knock) sensor with Piezo
If you want to make a simple touch sensor but you don't have the fancy ones around you can also u...
Grove - Ear-clip Heart Rate Sensor
Info & Arduino code https://wiki.seeedstudio.com/Grove-Ear-clip_Heart_Rate_Senso...
Capacitive Touch Sensor Breakout - Adafruit MPR121 12-Key
On this page you will find a tutorial for how to connect and use a Adafruit MPR121 12-Key Capacit...