WiFi booster

In cases like this, it is best to examine the building materials more closely. For example, it is just plaster, or is there a steel mesh in the wall supporting it?

One way to test is to use a WiFi analyzer app when you are in the same room, with the door closed, and then in 1 room over witht he door closed. The overall goal is to understand how much the wall is attenuating the signal.

Usually if there isn't much material to act as a faraday cage, then WiFI extenders can be a good solution. The issue comes when you have faraday cage like material in the walls. In those cases, while a modern Netgear WiFi router or AP will have some improvement since they consistently transmit near the FCC transmit power limits, and put a lot of R&D into optimizing the WiFI throughput over that range, there is nothing that can be done to provide a really good experience with a faraday cage. In those cases, you will need to either run Ethernet to the location where you wish to add an additonal AP (Nearly all netgear WiFI routers can be configures to work as a wired AP (same with their extenders).

If the material is not heavily attenuating the WiFi signal, thus allowing for a wireless extender to be decently effective, then units like their EAX20 will have transmit powers near the FCC limit, e.g., the EAX20 will transmit at 996mW on the 2.4GHz band, and 986 mW on the 5GHz band (the FCC limit is 1000mW but no bevice hits it exactly since with possibly variations in amplifier, and the issue of going over by any amount can cause it to fail certification, everyone leaves a tiny margin for variation.

A WiFi extender will maintain a stronger connection over a distance to the main WiFi router as compared to a client device since most client devices will only transmit at around 200-300mW, with many low powered devices such as phones other battery powered devices, using 100mW or less.