REDBACK COUNCIL - RISC

Misplace your phone in your own home but it's on silent mode? Lose a quiet tablet, but have no "Find My Device" app installed? There are a few ways to find your Wi-Fi enabled device if it's lost inside your sprawling abode. The Super Users at Stack Exchange provide some tips.

I lost my tablet somewhere in my house and have been searching for hours. It's an Android device, which seems to have Wi-Fi enabled (responds to pings), but doesn't seem to react to cloud-based messages. Furthermore, I have Cerberus installed on it, but cannot connect to it. Is there a way of physically finding the device by measuring the signal strength from different locations in my flat? I know it's theoretically also possible to triangulate a Wi-Fi signal, and even though I have four Linux based Wi-Fi receivers, I don't know any non-commercial software that is capable of doing so. 

Airodump-ng 

I know you can get the signal reception using airodump-ng (part of the aircrack-ng tool suite) if you have a compatible Wi-Fi card and a Linux distro up and running. You'll see somethinglike this with the signal reception listed as PWR (in decibels). If you keep pinging the device throughout this, you should see the airodump-ng screen update much quicker with the MAC address of the device. You should then be able to move around with your laptop, trying to increase the PWR until you find the device.

Homing Cone 

Something that may work: Go to the hardware store and buy some brass mesh and build a cone. You'll probably need to layer the mesh, then hold your phone in the middle of the cone. The brass mesh should block all radio signals, so if you get a signal, it's coming from the direction of the open area of the cone. In theory, you can use this to home in on the device. FYI, the brass mesh is one component in building a SCIF.

Ethernet & More 

Some Wi-Fi routers have a signal strength measurement on them. I know DD-WRT has this. If yours does, then you can do something like this:

• Get a long Ethernet cord.

• Plug one end into the router and one into your cable modem, internet connection, etc.

• Move the router around your apartment and see where you get the strongest signal. (Keep in mind, water pipes, metal studs, etc. can all distort Wi-Fi signals.)

• Another option would be to make your own directional antenna, kind of like this. You could also check out this page for some useful command line Linux Wi-Fi commands.

Triangulate 

One-story home? You can sort-of triangulate using signal strength alone. You have to assume that signal strength is proportional to distance from the transmitter, which isn't very accurate, but it could be accurate enough to help narrow down the search space. How to measure signal strength from 3 points in your house:

• On a floor plan of the home, mark your 3 points, and with a drawing compass, swing an arc across the flat with a radius proportional to the signal strength so that the arcs enclose a fairly small space within the home. 

• If the assumption we made were true (and your measurements and drawing were accurate), your tablet should be within the space between the arcs. It's not quite true but hopefully not too far off either. 

• Start your search near that space. Hopefully its location will remind you of where you actually left the tablet. If not, search out from there, possibly repeating the above steps at a shorter distance from this location.

• Multi-story house? Same idea, only now plotting is more complicated by the third dimension. Easier would be to repeat the above for each floor. Now you have two or three more spaces to search but that'll be more information than you had before.