Ever had a flyaway? Thankfully I haven't yet, but I'm always on the lookout for ways to prevent that from happening. So far, I know about 2 inventions that let you track your drone from a smartphone app:
Tile - $25 tracking tag with a hole that you can probably thread a wire through to attach it.
TrackR - they advertise it for finding lost keys, but it would be great for drone as well. Sticker attachment.
Others? Post 'em here.