Capacitive touch sensors, how do they work?
You can very easily make your own capacitive touch buttons. Texas instruments MSP430 has a good code base and PCB layout considerations for you to start right away.

The way they work, as better explained by the PDF linked above is as follows,


  "As shown, a PCB-based capacitor is formed between the center copper
  pad and the ground pour surrounding it. The electric field is allowed
  to leak into the area above the capacitor. The interaction of this
  sensor pad and the surrounding ground pour (also the ground plane
  underneath) create a baseline capacitance that can be measured. The
  base capacitance of such a sensor is in the range of ~10 pF for a
  finger-sized sensor. When a conductor, e.g., a finger, comes into the
  area above the open capacitor, the electric field is interfered with
  causing the resulting capacitance to change. The coupling of the
  conductive finger into the capacitive sensor increases the capacitance
  of the structure beyond the baseline capacitance, the capacitance of
  the sensor with no touch. By continuously measuring the capacitance of
  the sensor(s) in the system and comparing each result to a
  predetermined baseline capacitance, the system microcontroller can
  determine not only on/off button functions for each sensor element but
  also “amount” of press used for more complex interfaces such as
  positional sliders."


I recommend starting with the MSP430 LaunchPad and then getting the capacitive sense booster pack. You could be playing with capacitive touch for $15.