Any way to find a lost Kindle inside a house?

Question

I left a Kindle Paperwhite with my mom a month ago and it disappeared in the house, probably in between books somewhere. I know it still connects to wifi and receives documents through the kindle email at least once a day, so it has some battery left.

Is there any call home, lost beep, or similar feature I could use to help focus the search?

At worst I thought of setting up some laptops/phones sniffing packages and broadcast strength coming from the kindle's mac address (it shows up every once in a while in the router logs) and triangulate that to have a gross estimation of the location. Any idea on which software would be the most appropriate for it (ideally for ubuntu/android/windows)?

Thank you for your answers before the battery runs out

Answer 1

^{The OP's solution is below. Adding as a community wiki Answer and removing the solution edits from the Question.}

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Found the Kindle using the sniffing technique described below. However I'd still like to know if there's a way to find it that's less overkill.

I discovered that the Kindle updates its contents daily while in deep sleep around 5:30-6:30AM. So I set up the delivery of a biggish pdf file through the kindle email so I'd ensure a long enough connection, end set up three laptops with a Kali Linux running live with airodump sniffing packages (modified from here: http://www.androidauthority.com/capture-data-open-wi-fi-726356/ )

The following procedure can be used to physically find any active wifi device connected to a network:

Three lines of code in the terminal in at least three Kali Linux running devices (2D location, at least 4 receivers out of plane for 3D):

To start monitor mode on a wifi card (in this case wlan0, check on iwconfig if needed):

airmon-ng start wlan0

Airmon usually changes the card name to wlan[n]mon after this. Check the wifi interface name on iwconfig and modify accordingly if the next line returns a related error.

Then run airodump to find your wifi network and its channel:

airodump-ng wlan0mon

Enter Ctrl-C to end the capture once you note the desired network's channel

Run the following line to run airodump again only at the specified channel and record the data to the "allthedata.csv" file in the terminal directory (usually the root for a live cd/usb if you didn't change it). Replace the square brackets by the channel number:

airodump-ng -c [channel number 1, 6 or 11 usually] -w allthedata wlan0mon

I started the pcs before going to sleep and as I woke up a bit past the usual update time, I hit ctrl-C to stop the capture and looked up the device on the allthedata.csv files by its MAC number which can be obtained at the router logs. There are in fact 4 allthedata files with different extensions per capture, and on the xml you can find the manufacturer of the device in the logs, so even if you don't know the mac address by looking up an Amazon branded device connected to your router you may find the Kindle entry.

At the Kindle entry, find the signal strength value and note it for all the receiver computers. Then convert the values from dbm to mW using the following formula: mW=10^(dBm/10)*1000.

To triangulate the signal (for a 2D location), draw a chart with the position of the laptop wifi receivers and for every pair of receivers, draw a line perpendicular to the line going through the points in a point inversely proportional to the square root of the mW power values, as the signal drops of proportionally to the square of the distance (for 3D use at least 4 receivers and a surface between the points).

The lines should cross at the source of the emission - the Kindle was at a closet in this case. The margin of error was about 1m/3ft even with several concrete/brick walls in between the receivers and the emission.

Notes:

• This simplified location approach is only possible if the emitter is located in between the receivers, that is, a three-set of receivers (2D) form a triangle that has the emitter inside it.

• Different receivers might have different antenna gains and correcting for it will greatly increase accuracy. A quick and dirty way of doing so is positioning the receivers at the same position from a constant power emitter (wifi router, for example) and using the signal strength value difference between them as a calibration factor to be subtracted it from the signals received afterwards.

Answer 2

Let me share my solution here, especially as the ideas from this post helped me a lot.

So you gave me the idea that the Kindle updates its contents once a day so must connect to WiFi.
My router has no log about devices connecting and leaving, so I installed Android apps Fing and Easy WiFi Alert, both are capable of sending notifications when a device connects to your LAN. They also recognized Amazon as the manufacturer of my wife’s Kindle, helping me to match to the MAC address shown on the router's interface.

In Amazon.com you can also check what books/docs are downloaded to your Kindle, so I sent some large books to the Kindle email-address. By checking this page time to time I learned that books were downloaded between 9AM-10AM.

My router prints the signal strength of the connected devices, so I connected long LAN and power cables to the router, planning to hunt down my Kindle. I tested the method with my wife’s Kindle, strength was about -50db from another room, never below -40db in the same room and went up to -30 db close to the router. The next day I stayed at home waiting for the device to connect, and the above apps sent a notification when it did at 9:55, but I could only read the strength once without having time to move the router before the Kindle went offline. It was -51db, so I figured it must be another room...

So what I did was enabling a bandwidth limitation of 1Mbps for the Kindle on my router. This would mean that 1MB takes 8 seconds, 100MB 800 seconds, almost 15 minutes. I sent Pdf files of 100MB to the Kindle via mail.

Next day the notification came at 08:29. I moved around with the router in one hand any my phone connected to the router’s interface showing the stength in the other, recording my screen & selfie cam at the same time to be able to track back the values later.

However, wherever I moved in the flat, the strength never went above -50db. Since the suspect of the device’s disappearance was my 1.5 years old son, I tried the same in his height (1m), and the signal strength increased instantly. By moving around this way it went up to -25db helping me find a box in our bookshelf, behind which there was my dear, lost Kindle! The box was exactly under the normal place of our router, 1.8 meters below it - which gave the -51db first... It seems routers antennas aren’t facing downwards...

So quick tips as a summary, if your router can measure signal strength of connected devices:

• use phone apps like Fing or Easy WiFi Alert, which recognize the device’s vendor and send a notification when its online
• connect long power and LAN cable to the router, to be able to move around
• set bandwidth limitation in the router towards the Kindle, so that files take more time to download
• send large files to the Kindle’s mail address (with 1Mbps limitation 100MB takes about 800s)

Good luck and bye Peter