Identify Wi-Fi thieves with this simple app

The WiFi Inspector app promises to give you a quick snapshot of connected devices.

find wi lead image
Credit: Patrick Nelson

Recently, I was delving into my router’s settings menu, looking for a web-slowdown cause, when I came across something startling. There were about 25 attached wireless devices listed there. I only own about a half-dozen wireless gadgets.

A bit more detective work and I found that a bunch of morally-bankrupt, low-life freeloaders had hacked into my 5 GHz Wi-Fi signal. I live on top of a hill. The unfettered signal possibly propagated some distance; and the password was an easy-to-crack set of numerals.

Resetting the 5 GHz password kicked the poachers off. But now I regularly eyeball the Attached Devices list for imagined hoards of bandwidth pirates.

Time Warner Cable, my ISP, doesn’t need additional help providing stream slowdowns.

WiFi Inspector

WiFi Inspector is an app that I came across at XDA Developers that might make looter-detection a bit more convenient.

It runs on Android devices and simply scans any network to which the app-installed device is attached. It then provides a list of connected devices. That’s pretty much it. Simple, but highly useful.

There’s no need to fire up a laptop browser, enter a router user ID and password, or navigate uninspired router-settings pages. After an initial setup, the data squirts into the clean-looking app with a one-button “Update List” call.

Detailed information is provided for each found device, including IP and MAC addresses and device manufacturer.

With that information, you should be able to figure out which device is legit.


I was able to identify common devices on my network easily, like a laptop, my Android phone and tablet. Some vendor names listed were obvious, like that for a Sonos music system, labeled “Sonos,” as one might expect.

In depth

However, one IP address was ambiguous, so I launched the usual router-interface on my laptop and cross-referenced the WiFi Inspector app-listed MAC address, with the router interface-listed Device Name. I found the perp was a known device — a spare phone.

Using the MAC addresses for unclear items like that, I was able to ID all of the attached devices and mark them as “Known Devices” in the app.

All of them were legitimate this time, and I think that further ad-hoc scans should quickly identify unknown devices, which will alert me to investigate.


My only criticism is that wired devices show up alongside wireless devices in the list, and subsequent elimination of those wired devices added to the workload. It would be more efficient if wired devices were ignored.

After all, wireless intruders will only appear on a Wireless Devices list.


Faiz Malkani, who writes for the All Android blog at XDA Developers, directs users to the WiFi Inspector application thread—also at XDA—which is an ongoing discussion related to what devices work properly with it, and so on.

Why wireless intrusion could be an upcoming problem

In my case, I was stung by my switching on of the less-common 5 GHz radio, and not securing it properly.

That 5 GHz Wi-Fi, with its 2.5-inch wavelength, has certain propagation characteristics, which, it can be argued, are well-suited to future Internet of Things.

This is partly because there’s not as much interference as with established 2.4 GHz—the usual Wi-Fi block. That frequency is also used by numerous legacy devices, including microwaves and baby monitors, so it is saturated.

And Wi-Fi at 5 GHz’s, short wavelength, works well in line-of-site cases, but not through walls, so it is more secure for one-room setups: for example, your Wi-Fi-enabled fridge won’t yak with the neighbors’.

Plus, the fact that the signal doesn’t spill over to the neighbors means more efficient spectrum usage. More data can be carried on the same frequencies.


The problem is that although 5-GHz signals travel shorter distances inside, they can, in some circumstances—like when coupled with good antennas and a lack of interference—travel further outside, where there are no obstructions. Although theoretically, the shorter the wavelength, the shorter it goes.

In my case, the 19 poachers, I believe, were clearly not coming from abutting apartments. This is because the odds are against it—too many disparate devices, and the fact that the signal barely gets through the walls anyway. The hijacks had to be coming from outside via windows and the unencumbered view.

So, couple future 5 GHz router switch-ons with user-friendly, easy-to-remember password creation, and wireless bandwidth theft could become an increasing problem.

At least if you live or work on a hilltop. As, I believe, my neighborhood bandits discovered.

Join the Network World communities on Facebook and LinkedIn to comment on topics that are top of mind.
Must read: 10 new UI features coming to Windows 10