Answer: Three miles.
Currently in the midst of a crowdfunding campaign, Lynq hopes to be able to replace those unreliable cellphones and unwieldy GPS devices when you need to find someone in a hurry. While its most obvious uses include outdoor adventures like skiing and backpacking, Lynq could also be useful for concertgoers lost in a crowd or parents who want to easily keep track of their kids.
Each device can be named after the user, and a maximum of 12 devices can be joined on the same network. To find a certain device, and the person carrying it, simply cycle through to their name and the device will point you in the right direction and tell you how far away they are. There is also the option to set a boundary for certain devices, so a parent could be notified if their child strays too far.
See Lynq in action in the video below.