
Lost and Found: Stopping Bluetooth Finders from Leaking Private Information - adulau
https://arxiv.org/abs/2005.08208
======
lwneal
These tiny coin-cell-powered Bluetooth tags are great for tracking your lost
dog or stolen backpack, but they can do lots of other things, too!

They can measure temperature, acceleration, and magnetic fields, so you can
use them to detect when a door or window opens, whether a machine is
vibrating, or even an object's orientation relative to magnetic north. All
this can be done for years on a single battery charge and at a cost of pennies
per sensor per day. If these devices become 10% smaller each year, it's easy
to imagine them eventually becoming something like Smartdust [1].

You could stick one on a treadmill or a weight machine to see how often it is
used. Put one on your refrigerator door to find out how often you open the
fridge. Put one on your office chair and track how many hours you spend
sitting in your seat. Stick one inside a utility panel or a locked door and
get an alert whenever it is opened or rattled. The possibilities are endless.

However, there are two truly difficult problems to solve in the design of a
bluetooth smart tag: security, and battery life. Sadly, they often conflict.

For example, it turns out that Bluetooth radios consume battery power not just
when transmitting, but also while _receiving_. If you treat the tag as a
standard Bluetooth device and allow it to receive and transmit, you're solving
the easy security problem.

But if you want to build a _really_ good tracker with maximal battery life,
then you have to solve the hard problem: the tracker has to spend most of its
time operating as a broadcast-only beacon. That means that every passing
receiver can't send challenges or requests: the tracker can only yell its
encrypted data out into the void.

The system proposed in this paper is a great improvement on what companies
like Tile and Nut are doing. But I predict that Bluetooth smart tags won't
really take off until someone solves the "hard" problem.

[1]
[https://en.wikipedia.org/wiki/Smartdust](https://en.wikipedia.org/wiki/Smartdust)

~~~
gruez
>They can measure temperature, acceleration, and magnetic fields

There are cheap bluetooth tags that have a thermometer, accelerometer, and
hall sensor built in? How much do they cost and where do I get them?

~~~
kayhi
I'm also interested on where to buy tags for pennies even if they only have
Bluetooth.

~~~
oarsinsync
> All this can be done for years on a single battery charge and at a cost of
> pennies per sensor per day

Assuming pennies and years both (as plural) == 2, you're looking at a minimum
of $14 per sensor.

$15-30 feels like the right ballpark, so OP is in the right area.

~~~
kayhi
from where or are there brands you recommend?

~~~
oarsinsync
I'm mostly in the zigbee space, rather than bluetooth. Aquara / Xiaomi have a
load of cheap sensors available on aliexpress. Get yourself your own zigbee
dongle (suggestions at
[https://www.zigbee2mqtt.io](https://www.zigbee2mqtt.io), no affiliation, also
available from aliexpress) and you have no vendor lock-in either.

