[NNagain] bluetooth occupancy sensing

[dan]

I also have bluetooth occupancy sensors lol.  We have a lab test going of
triangulated bluetooth tag locating.  So you put a BLE tag on a device and
*3* or more receivers in a space at different locations and heights which
are documented and then BLE tags are triangulated based on RSSI.  Having
sensors at various heights allows for tracking even the 'z' axis.  These
tags are very cheap, you can buy complete tags for a couple of bucks, don't
even have to build your own, and you can get them built into cutable (or
non-cuttable) wristbands.  You can also do short-term tracking of cell
phone beacons, though privacy mode means that you only get a short
'session' with a phone (because of privacy mode on newer phones) that isn't
paired with something but if you have a phone with a bluetooth headset, the
'locks' the bluetooth mac address and now you can track the phone anywhere
that the bluetooth headsets follow.  You can also track cars which don't
scramble the mac, but you get cars with wifi mac as well.

We can get bluetooth to within inches accurate when it's line of site.  In
a pocket or something it's about a meter because bodies/clothes etc reduce
RSSI unevenly.  The purpose of this is a couple of things, 'patient
tracking' in any sort of a facility like nursing home or hospital, and
device tracking, again in a facility with shared hardware like portable
EKGs and handheld XRays etc that get 'misplaced' and staff has to go on a
hunt for.  It's also much cheaper than lorawan as BLE transmits many times
a second and runs for years while lora is built for more range and only
transmits intermittently, usually 10-60 minutes to preserve battery.

We're testing mainly on dragino and milesight devices.  I'm also having
decent enough luck with mikrotik's knot which can track BLE beacons with
high enough precision.  Mikrotik has their own somewhat expensive BLE
beacons also but these are basically universal.
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