Based off of the FreeScale MPR121, the I2C Touch Sensor is a module used to detect the touch or proximity of human fingers. This sensor includes 2 parts: one Touch Sensor controller, and 4 finger "feelers". It's easy to set up: insert the connectors of the "feelers" into the base of Sensor controller and you can begin your touch controlling.
MPR121: The MPR121 is a capacitive touch sensor controller which features internal intelligence. Includes a hardware configurable I2C address, an expended filtering system with debounce, and completely independent electrodes with auto-configuration built in.