How do I get my VCR to record when someone comes into my room?

[foolellelaclunk]

I want to set up a CCTV type thing in my bedroom. I have a camera its one of those ones you put outside your front door and when someone walks in front of it, it turns on and comes up on aux channel on ur tv.

What I want to know is how do I get my VCR I start record g when someone comes I to my room when I'm not around.