This Touch Switch circuit use a part compares with voltage 2 group , within the integrated circuit timer LM555 or NE555. For perform wait for catch the change of voltage , which be born from way leakage touches by change a finger. When the value is Resistance at drop the pate which build with pin 2 of the integrated circuit is valuable are down the level is Voltage output (pin 3). Will have the condition voltage high for apply the work and other circuit next. The detail is other , a friend sees in the circuit yes.