Google’s “Find My Device” function does a pretty good job of finding a device. It has a few mechanisms:
- GPS location seen by the device (pretty accurate)
- Cell tower location (not very accurate at all)
- Wireless access point locations (quite broad)
- Quick connections by bluetooth to passing android devices on the “Find my device” network (could be accurate, but is not).
That last method, bluetooth snitching, produces some interesting results.
I dropped my phone by accident, and discovered it missing when I got home. I took the precaution of using the “secure my device option”. The next morning the phone went for an unauthorised walk, presumably because some helpful soul thought he would find the rightful owner as he went about his day.
Find my device reported its location in a number of interesting places:
- In the actual place where it was found 👍
- A little way up the road on a nearby highway 👀
- On the other side of the road from where it was found 👀
- 1km down the road from where it was found 👀
- In a suburb 6km away 🤪
All of these locations were reported as 100% accurate – but they were not the location of the phone (except one), but the location of the snitch phone that had recently seen my phone … and then moved. The information about how long it had been since it saw it, and the strength of the signal is discarded.
Here’s the faulty logic:
- Bluetooth message: “Hi, I’m a lost device: please report my location”.
- Gallant helper on find-my-device network: “Sure, no problem.”
- Gallant helper: Oops, don’t have network right now.
- Gallant helper: Hey, I’ve got network! Let me report my current location.
- https://www.google.com/android/find/ : Hey, your phone is on the highway in a car zipping around a corner. No wait, it’s in another suburb. No wait, it’s in that shed. No wait, it’s on the other side of the road.
The moral of the story is: don’t issue search warrants without complete technical information. If you suppose that a man is handling stolen goods based on “find my device” then the evidence may actually show that he was merely at some time in the vicinity of stolen goods.
But, just this once, it was found!
