Hidden Treasure Box Idea

Hi, I have a very rough idea for a kid's game like a treasure hunt. It would involve at least 2 boxes with Arduinos. One would contain the treasure and one would assist in finding the hidden treasure box. I imagine the assist box would have an lcd screen and give the user clues. The treasure box would possibly contain a speaker for sound when the treasurer hunter is close enough.

I have seen the GPS enabled treasure box that only open when in a certain location. My idea is for someone to put treasure in a box and then hide it around their house or outside. The treasure hunter then uses the other box to find the treasure.

My question is this: What is the best way to allow the the two boxes to "communicate"? Bluetooth? GPS? Xbee? I imagine you would need at least 50 feet so that may rule out Bluetooth. I'm not sure how far that goes.

It would need to be able to calculate a distance as to give the treasure hunter clues. What do you guys think? Is my idea possible?

Thanks.

How would they know they are close to each other? Think distance measuring would be important here.
Could use simple 315/434 MHz Tx/Rx modules, <$10/pair.
Not sure what you’d for signal strength, GPS location comparison, something along those lines.

Maybe put a hidden PIR in the treasure, it can start transmitting a different signal when something sets it off.

Yes, distance measuring would be important. Do you have a link to the 315/434 MHz Tx/Rx modules CrossRoads? I like the PIR idea too. I found one for under $7.00 http://www.futurlec.com/PIR_Sensors.shtml

Sparkfun carries RF again, and this place has several to choose from http://www.robotshop.com/433mhz-high-sensitivity-transmitter-receiver-pair-rxa30.html

Yup, Sparkfun has them as well. http://www.sparkfun.com/products/8945 I also found a helpful tutorial for us Arduino folks. http://letsmakerobots.com/node/12336. I've never used these modules before. I'll give it a try if I ever complete my current project.

Thanks Crossroads.