This Robotic Car is a great introduction to soldering as well as the
basics
of sound control and mechanical motion.  The car has a electret mic
that
feeds noise to the control circuitry.  When a loud enough sound (like a
clap) is heard it will cause the car to stop moving forward and reverse
itself turning slightly left for a few seconds.  Then the car will
resume
forward motion in a different direction.  You can adjust the circuit
sensitivity so that very soft or very loud noises will reverse the
motion.
Specifications:

Power: 2 AAA batteries (not included).
Includes sound activated circuit.
Circuit board requires solder assembly.
Unassembled printed circuit board Soldering required.
Learn motor theory, transistor switching and R/C time constant
circuits.
Changes direction with a loud sound such as a whistle, a clap or when
it
hits an object, it will then automatically reverse itself for a preset
time
and then resume its new course.