THE INVENTORS OF BLUETOOTH SAY THERE COULD BE PROBLEMS USING THEIR TECH FOR CORONAVIRUS CONTACT TRACING
https://theintercept.com/2020/05/05/coronavirus-bluetooth-contact-tracing/

I asked Jaap Haartsen and Sven Mattisson, who invented Bluetooth together while working at the Swedish telecom Ericsson, whether their tech was up to the task. While both expressed hope that Bluetooth could be used to save lives, they also noted that problems of accuracy are very real. Bluetooth Low Energy, or BLE, a more modern iteration of the tech that’s a great deal more efficient and accurate, and which is used in the Apple/Google contact tracing system, is still subject to finicky physics.

“One issue that comes to mind at the physical layer is the uncertainty in the detection range,” explained Mattisson, “i.e. how well can you assess the distance to another BLE device. … The radio signal’s path loss will vary significantly depending on conditions (i.e. free space or obscured). Whether knowing the distance only within a factor of, say, ten is a problem or not, depends on the application. E.g. do we get too many or too few contacts…? Temporal aspects can be used to reduce this uncertainty but it is easy to forget about the coarse range resolution of a single radio link.”

 

Ineffective, just like the inventors said.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0239943#sec017

Abstract
We report on the results of a Covid-19 contact tracing app measurement study carried out on a standard design of European commuter tram. Our measurements indicate that in the tram there is little correlation between Bluetooth received signal strength and distance between handsets. We applied the detection rules used by the Italian, Swiss and German apps to our measurement data and also characterised the impact on performance of changes in the parameters used in these detection rules. We find that the Swiss and German detection rules trigger no exposure notifications on our data, while the Italian detection rule generates a true positive rate of 50% and a false positive rate of 50%. Our analysis indicates that the performance of such detection rules is similar to that of triggering notifications by randomly selecting from the participants in our experiments, regardless of proximity.

https://www.wired.com/story/google-apple-change-tactics-contact-tracing-tech/

IN APRIL, APPLE and Google announced a rare act of tech giant fraternalism spurred by a global pandemic. Their plan tapped the short-range Bluetooth signals from smartphones. Phones would keep track—anonymously—of other phones they were near. When the owner of one of those phones was diagnosed with Covid-19, alerts would be sent to others who had recently been nearby. The idea was to help public health officials more quickly track down potentially exposed people and stem the spread of the virus.

Most states have decided the tracing API is useless outside of the APPLE & Google laboratory.