A schematic diagram of a touch switch circuit is shown below. This circuit consist of timer, one shoot multivibrator and touch terminal. As timer, this circuit uses 555 timer which is connected to one-shot multivibrator. The touch terminal is used to trigger this circuit. The output of this  circuit can be used to drive a power transistor, CMOS circuitry, hexFET transistor or optocoupler. Here is the schematic diagram of the touch switch circuit:

Touch Switch II circuit schematic

Using the given values as shown in the schematic diagram, this circuit has timed ON period of 4 seconds. The value of C2 and R3 determines the ON time, increasing the value of C2 or R3 will increase the ON time. The ON time is decreased if the value of C2 or R3 is decreased.