I just installed a BLE scanner. I don't have any BLE device turned home right now. I can pickup about 20 devices from my neighbours, from my building and across the street. I don't interact with them but the app may decide I'm at risk if they're sick #COVID19 #ContactTracingApp

Because developers want to restrict the distance, they will only look at the highest RSSI. Let's do that. I'm not moving, and we can suppose most other devices aren't drastically moving.

Yet after one second, you can see how different the picture looks. Another second later, this is also different. Now imagine how it will change in 10-15 minutes in the real world when you are moving, other people are moving and you have moving obstacles.

And now after the time it took me to write this thread. So different! Bluetooth contact tracing apps are based on incorrect/unscientific assumptions. This is aside any privacy/security consideration. For more information, refer to my previous thread: https://twitter.com/clevybencheton/status/1250830594793185281?s=20

And look at my battery levels in 5 minutes. That's never going to work in real life. Nobody will want to end up with a dress smartphone during their commute, particularly in metropolitan areas with large scale public transport where this kind of app was supposed to make sense.

A dead smartphone*