First off, the OS X Wi-Fi Diagnostics utility is not new per se — it was part of OS X Lion. Nevertheless, whether you are looking for an automatically updating image of your Wi-Fi activity or a detailed, in-depth examination, Apple’s Wi-Fi Diagnostics is very cool and one of the hidden gems in OS X Mountain Lion.
And, by “hidden” I mean the average user won’t be able to find it just by digging around inside their hard drive. That said, in the Finder, choose Go to Folder under the Go menu, or press Command + Shift + G, enter this path “/System/Library/CoreServices/” and then hit Return.
From the resulting window, find and then Copy/paste or drag Wi-Fi Diagnostics into your Applications folder or Launchpad — keep it handy. Also, while you are in there, have a look around as there is a ton of useful stuff in the Core Services folder.
Open Wi-Fi Diagnostics. Now, if you want a hard-core, data-rich look at your Wi-Fi usage, as well as the networks around you, then click Create Diagnostic Report and click Continue (above), but be warned — you don’t get one report and you have to open them in another app, such as Console.
If you just want to look at a pretty, self-updating picture of your Wi-Fi data use and signal strength, then select Network Utilities (Command + N, image below)
Sadly, the only detectable Wi-Fi network at my house is my Wi-Fi network.