I really want to know if this kind of product exists commercially:

Something that allows you to be able to tell how far an object is from you in miles. I don't care about the map or direction (GPS -use of satellite which most people don't have access to), I just care about the distance. Just something cheap that you can plant in a car so you will know how far the car is away from you at all times within a 5-10 mile range.