Many might already know that congress recently signed the Federal Aviation Administration Re-authorization Act, which orders the FAA to make way for drones in the National Airspace System (NAS) by 2015.
It seems that the rules will remain the same for recreational drones flying below 400 feet (which constitutes the vast majority of activity on this site). But for those seeking higher altitude, it's likely that your drone will need some kind of "sense and avoid technology."
From the bill, H.R. 658:
SEC. 322. CIVIL UNMANNED AIRCRAFT SYSTEMS INTEGRATION PLAN.
(a) Integration Plan-
r the operator and pilot of a commercial unmanned aircraft system, including standards and requirements for registration and licensing;
To create a small Unmanned Aerial System (sUAS) with sense and avoid technology, you need to make sure that the equipment is small. sUASNews.com recently made a post about the world's smallest FAA-spec transponder. It measures 3.5" x 1.8" x 0.7", and weighs about 100g - which is 30 percent lighter than an iPhone.
The transponder is based on Automatic Dependent Surveillance-Broadcast (ADS-B) technology, which compliments the FAA's switch to the GPS-oriented "NextGen" system. All aircraft in the NAS must be equipped with ADS-B transponders by 2020.
It runs on 10-32V, and consumes about 8 watts during normal operation. Not sure about the cost, but I'm attaching a nifty PDF with more info about the device.Sagetech-XP-Family-Transponder-Brochure-v3.1.pdf