That's a nice gadget, that's it. You won't use it in the real world when something like that is really needed, because nobody else around you has one. Plus: your cellphone will barely last one day even in standby mode and you will soon discover that coverage for that thing is god-awful with obstacles between both parties. We are talking about a reach of 30 meters, you might as well be shouting to your neighbors instead of using fancy devices. Real-world useful tech are sneakernets.