Problem statement for my project regarding motion sensor

first of all i want to appologize if im posting at wrong category

im currently doing a project regarding study n develomnt of motion sensor but my problem is what would be the appropriate prob. statement, since im just doing a stdy n then develop a motion sensor.

thanks in advance

There are three major approaches used for motion sensors: using infrared, using microwaves, and using sounds or ultrasounds.
Each approach has pros and cons. Just search the net for more information on each.