Brother range extender range? Router model Netgear ac1750

A brother range extender keeps popping up on my wifi . Meaning I can see them and they can see me . My question is this. The nearest house to me is at least 1000 feet away. Also on my nighthawk app I have this phone and my Verizon range extender that is all. But a 3rd devise keeps popping in and out. Should I be thinking someone has highjacked my router?