I used a cool touch sensor call MPR121 in a project I did a while ago. It is a touch sensor controller, which detects small capacitance changes when a person touches on any conducting materials that are connected to its electrode ports. My team and I hooked up the electrode ports to different fruits, and turned those fruits into buttons. Then the sensor is hooked with an Arduino board controlling a speaker. We made it a fun game: people can play the fruits like piano keys, or people touch fruit as instructed by speaker.

One tricky part of programming MPR121 is that you need set the right amount of current depending on the material you used as electrodes. If you are interested, see my summary on the FruitSpiral page.