trying to build a wireless alarm system off a motion detector. How do I alert the mobile remote, radio frequency?

how do i builder a radio frequency to alert my wireless remote that the motion sensor has gone off? can someone please explain the whole frequency to me?? very urgent would really appreciate the help! thanks for your time over looking my problem.

Frankly, you don't. RF work is not for a beginner in electronics ! You can buy the functions you need for a lot less than you'll ever make your own system. Look at Zigbee modules for a solution - and then look at the prices people like X10 and various Chinese firms will charge for the whole thing.