This analog circuit is comprised of two parts: an astable multivibrator that creates a low-frequency square wave (left side) to switch on/off a Darlington amplifier (right side) that drives the pager motor. I have added various capacitors and a resistor to the amplifier stage. These affect the quality of the motor speed, making it turn on and off more naturally. The video shows me removing / replacing the pull-up resistor on the emitter of the second NPN transistor, illustrating its function (to provide a baseline motor speed so that the motor does not come to a complete stop, but instead undulates between a faster and a slower speed).