Hi Picers!

I am a software/web developer, and only know the very basic electronic stuff.

I have develop a few small electronic projects with a LCD, keypad, EEPROM etc and using picbasic to control all of it. So my knowledge is limited.

I'm struggling to get a good night's sleep because I always hear things outside, so what I want to do is to develop a wireless motion sensor.
My Door chime is wireless and can work up to 100m. I have opened it and the electronics look fairly simple.
I'm not sure how I will be doing this and where to start.
I want to create a couple of units that each has 2 sensors in, 1.2 meters apart so that it only picks up people (Each Unit will be a zone)
It must then send a signal to a main unit that lies next to my bed.
The Main Unit must only make a beep and switch on a led for the zone that was triggered.

Is this a difficult project?
Any ideas where I can get started?