Greetings. My name is Jeremy Trammell and I represent a group of developers and designers in Portland, Oregon. We have extensive experience with the Arduino platform and would be happy to assist you with your attempt to determine proximity via BlueTooth signal. Since BlueTooth is not designed as a "proximity sensor", I'm not sure how satisfied you will be with the end result, but by tracking the RSSI decibels in theory you will see a relative change with distance from the transmitter (i.e., a certain signal strength will not always mean the same distance, but at any given moment in time a lower signal strength will indicate an increasing distance relative to the previous reading). Will you be providing the hardware, or should we add the purchase price of the hardware to our bid?