Trap Detector

I have a project in mind where I create a "trap" and tag it with a RFID chip coded "Trap". I then want to create a device that starts to glow when it gets within a certain radius of the "trap" and get brighter the closer it gets. How hard would this be? How expensive would the components be? Are these devises good enough to only be triggered by a "trap" tag and not a "treasure" tag?

DigiOz