Aarogyasetu_android: False positives by bluetooth proximity

[samiullah]

As an end user If my neighbour who lives around 50m away from tests positive, app shows that U r at risk. Since most of Smart phones are using Class B bluetooth modules, there must be a range class which filters proximity range to 6m only. So if any user comes in 6m range of patient he should be sent an alert of high risk.

[gulshan98125]

I can't seem to find the filter being applied to the bluetooth proximity detection in the source code too.

[samiullah]

They are using default range of bluetooth of phone, that needs to be fixed

[gulshan98125]

Exactly! This has definitely created so many false positives. Threshold on RSSI could have reduced the false positives by a lot. I wonder how did they even released it without an RSSI cutoff!
Edit : I found that they have set the transmission level as ADVERTISE_TX_POWER_ULTRA_LOW which has broadcast power of approx -21 dBm .
But still this doesn't justify that we can't receive a signal at longer distances creating false positives.

Also I think 6 m is too much to give high risk info. It should be around 2-3 m. The stronger is the signal the more we can assure about more true positive and low false negatives.
I have raised a pull request for the same. Lets see if they approve it.

[samiullah]

thanks @gulshan98125! I have written 6m as there are some cases/research going on wherein they have found droplets can travel upto 20 feet.

[ritwikmishra]

@samiullah @gulshan98125 if the bluetooth scanning distance is 6m per device then bluetooth proximity per device becomes 12m (because both devices will be scanning in 6m area). Generally, one-floor height is ~3-4 meters. And since both the floors will have same Lat Long, will it give alert even if two people are separated by floors?

And I suppose if this indeed is the case
then it can start a chain a reaction where all the residents of a multi storey building will come in high risk, even if resident of one apartment gets positive (due to external factors).

radio waves can still pass through objects, even concrete walls and floors, meaning that a Bluetooth signal is not limited to the room you’re in. - source

[gulshan98125]

@ritwikmishra Bluetooth proximity per device will still remain 6m and not 12m because a device will only detect other device placed at 6m.
Also walls reduce signal by a lot so the signal received at 6m won't be the one equalivalent to in open space. Hence it will say that distance is >6m since distance is calculated on the basis of signal strength.
About the chain reaction, it won't happen because Aarogya only informs another user when he comes in contact with covid+ and not with the one who was identified as risky by the app.

[ritwikmishra]

Hence it will say that distance is >6m since distance is calculated on the basis of signal strength.

@gulshan98125 can you point me to the specific part in the source code where it calculates the distance on the basis of signal strength?