A wireless hydrometer inside a fermentor full of liquid inside a metal box (a fridge) is a fairly challening environment to get a decent wireless signal out of. A wireless network extender was called for. I did some research and there were some good reviews of the NetGear AC750 Wifi range extender
My brew shed is about 10 meters from my house and the wireless signal is fairly weak at the shed door, and is fairly intermittent inside the shed. Close the metal door and we are almost in a Faraday cage environment.
The extender only just manages to connect to the existing wireless network inside the house. This is denoted by the red light on the extender plugged into the GPO. So the way it works is the device connects as a normal wireless client to the existing WiFi network. It then creates its own 5Ghz and 2.4Ghz wireless networks which you connect devices to. It passes through network information from the main WiFi router to its clients.
And here is a photo of inside my shed. Excuse the rat's nest of wiring on to of the black fridge. I am testing out colling systems for my conical fermentor outside of the fridge. All a bit of a prototype at the moment.