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Comment by michaelt | Hacker News Reader

Does the indoor location feature work on time of flight, RSSI or something else? If it's time of flight, how do you convince the OS to give you accurate enough time measurements?

The website claims 3 year beacon battery life - but bluetooth has a reputation for poor power performance. How often do the beacons broadcast, for how long, and at what power output?

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It works by RSSI [1], and I believe you can calibrate it with your antenna/case design. Not to mention any attenuation by the phone's antenna or your hand/body.

Quote:

"Phones or other smart devices can pick up the beacon’s signal and estimate the distance by measuring received signal strength (RSSI). The closer you are to the beacon, the stronger the signal. Remember that the beacon is not broadcasting continuously—it’s blinking instead. The more frequent the blinks, the more reliable the signal detection."

[1] http://developer.estimote.com/

Beacons use the newer Bluetooth 4.0/'low energy' specification so they're not like old Bluetooth devices that are constantly connected. It's up to each beacon to decide how often it broadcasts, how powerfully, etc. Check out BLE SoC's like the Nordic nRF51822 for examples of hardware that could turn into a beacon without a ton of work.

We're doing sensor-fusion trying to use as much data as possible coming from different sources, so besides RSSI from beacons there's also accelerometer, magnetometer, etc. Lots of non-trivial maths to combine that into a robust model, but results are getting more and more incredible. :)

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