In Linux you can install two applications, “etherape” and “zenmap”, which will graphically provide you with a lot of information. Etherape is a network traffic browser which shows all of the hosts connected with your LAN router. Zenmap is a GUI version of “nmap” mentioned previously, and allows you to scan IP’s connected to your LAN to get more information about them. I find, though, that I can get information about devices connected to my wifi by browsing into my router and looking at the status of all the wifi connections. It shows both active and historically active devices, and I would notice quite quickly a computer or device not in my household. Much of the information provided in the example apps in the article looks much like what I find directly on my router. You just need to access your local router’s IP and browse to that. I think most modern routers are web enabled for administration.