How would you get a motion sensor to move with you?

Question

I'm doing an invention for a science project and I need a motion sensor that could be rigged to move with you.

Answer 1

You would need a stepper motor and a controller.
You would need to write a program to lock on to the motion.

There are some commercial units out there. Many are used for cameras.

Answer 2

you can use the principle of closed loop systems by making two sensors that detect motions and sum their output int an OP amplifier and feed the signal into a dc motor
let D1 and D2 so the normal output is 0 when D1 operate The OP will give a + signal so the motor will turn clockwise.
if D2 operate The OP will give a - signal so the motor will turn anti - clockwise
this is a very basic idea and i hope it will inspire you for a more complected system