RADAR discovery circuit !!!! help !!!

I AM THIKING OF THIS PROJECT . I WANT TO BUILD A CIRCUIT WHICH CAN BE USED IN CARS. I WANT THIS circuit to give any kind of alarm when it reach area of radar .i am trying to get the start points or any things which can help me and i didn't find any thing to start with . please if u have any think to share with me tell me ,. iam waiting >>>> thanks for ur time and consideration. :?

You mean a radar detector?

Why not just take apart an old radar detector......you still see them at garage sales and flea markets.

...there are about a million on EBAY too!

Good luck