razer following robot

hi. i want to make a razer following robot, and have a question.
although i searched google, there is no project that follow razer pointer.
what sensor should i use to sense the razer?
can you recommend the variation of sensor and product name?
i'm sorry for poor english

A "razer" is something which razes, i.e. completely destroys.
A "razor" is something which cuts, like a razor blade.

I wouldn't want to follow the former, and I wouldn't want a robot in control of the latter.

What are you trying to do?