seemoo-lab
Tell me about the `confidence` key
Hi all,
Haystack reports have a key called conf. I’ve seen it go as high as 115. What is this number telling me? What’s the scale?
My best guesses are:
-
it’s the dBm of the beacon’s signal. This would allow a very rough estimate of the distance between the tag and the iPhone.
-
it’s the estimated distance, in feet, between the tag and the iPhone sending the report. Using this as a confidence radius produces reasonable results.
I think the first is most likely, but the second produces reasonable ranges.
What am I missing or don’t know?
Thanks in advance
I'm also curious to know what that piece of data means, but my best guess is that it's the estimate distance between the tag and the reporting device. Anyone?
I get confidence values up to 220 ... my guess is the distance to the tag: the closer the higher the more accurate the gps values. I believe it is based on the strength of the signal (dBm) which can be used to measure the distance.
If we could intercept what an original airtag returns back via API and what's shown in original map as radius then we could reverse engineer it.
Just read in the author's paper that it likely represents the accuracy in meters. If you open google maps and look at yourself it shows a blue circle – "confidence" being the diameter of it – if I understand it right.
Paper doesn't give details on confidence. But GPS comes from the finder phone not from the tag, so maybe it's related to BLE RSSI e.g. -115dBm
would be easy to reverse engineer it, do 5 measurements via the network, meters vs confidence value, something like 1m, 5m, 10m , 15m, 30m I don't think it goes further.