&gt; I have a GPS unit sitting on my desk right now that I could swallow if I put some effort into it.<p>They aren&#x27;t that big. Many FPV aircraft carry GPS units for automated return to base functionality and crash recovery. However, there is a significant number of UAVs that are extremely light and weight sensitive (microquads and ultralight gliders).<p>&gt; any model aircraft that can&#x27;t carry the weight of a GPS unit itself is won&#x27;t pose a threat.<p>Right. It is quite likely that any requirement to carry transponders will be associated with certain weight limits and&#x2F;or flight types. UAVs that will operate out of line-of-sight or that will operate autonomously will likely (and should) be required to carry transponders and have additional licensing&#x2F;registration&#x2F;insurance.