The touch sensor circuit is a very simple design made of little electronics components like transistors c1815,resistors 1k,battery.
The circuit needs little explanation because it's simple to design it's works on the principal of touch when you touch the emitter and base terminals of the transistors the small led bulb will glow, the led glows on the force applied on those terminals that is when you touch it a little it glows a little and vise versa. The can be used for many purpose in electronics like simple led lamp circuit etc.
Thanks.