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1) GPS is not precise enough, especially indoors. You must use something else. All you've got to "measure" with is the signal strength. Phones vary a lot in their transmitted energy, and you don't know which model the other person is using, so you can't tune it from the phone model. Antennas vary greatly as well, an they do not distribute the energy evenly over a sphere. Turn the transmitting, or the receiving, or both phones 90 degrees around each of the three axes - received signal strength may vary considerably. At chip level, many (most?) BT chips allow the transmission power to be adjusted. I don't know if this is available through Android, but if it is, it adds yet another factor in signal strength: Even if you knew the exact model held by the other person, you wouldn't know the raw transmission power.
2) Draw two lines, 6ft apart, and have two people walk towards each other immediately outside the lines. Put their mobile phone in the pocket towards the lines. Let us optimistically assume that both phones report a distance of 6 ft. Then repeat the same test, but now with the phones in the pocket facing away from the lines. Persons meet at exactly the same distance between them. Not only are the phones about 4 ft further apart (2 ft on each side), but also, the signals must go through 4 ft of human flesh, 2 ft on each side. Which distance will the apps report this time?
Bottom line: Distance estimates based on BT signal strength is a joke.
3) You may have been infected up to two weeks ago, in the worst case. For those two weeks, you have been walking around spreading the virus. Even in the best case, within reasonable limits, will it take a couple of days from that other person infected you until he notices any symptoms, either get really sick, or he lines up for a test, which takes some time to analyze, and to get the message back to that other guy, so that he can warn others that he might have affected them. If you were infected, you would be spreading the virus for at least a couple of days.
4) The other guy, who infected you. must himself take the initiative to report to a central cite that he has become sick. Chances are that if if the illness comes very rapidly, chances are small that the first thing he will think of is fiddle around with his smartphone to report to a central site; he might forget it entirely. Furthermore, you must regularly interrogate the central site about all the people you have met, whether any of them have turned sick. So there is another delay, and reliance on explicit actions.
5) You and the other guy must report to the same central site using the same protocols.
6) Very few of my enocounters with other people last for 15 minutes. The great majority are shorter than two minutes: In the streets, at the gas station, in the grocery store. For my family, I don't need an app to tell me that we are close.
7) Everything relies on you always carrying the phone in your pocket, that BT is turned on, that the phone has not run out of battery power. It relies on the other fellow not having left his mobile at home or in the car, that he as BT turned on and has not run out of battery. I am among those who very often to not bring my mobile with me - sometimes deliberately, sometimes just because I forget it.
You describe a solution where you do not poll the central site, but the central site "broadcasts" (it isn't, technically speaking) sends out a push warning to each and every one. In the USA, with at least 200 mill smartphones (probably a lot more) and almost 0.8 million cases, if this system had been active all the time, everybody using it, something in the order of 160 trillion messages would have to be sent out. You must have some way of filtering this, but the central cite knows nothing about who the now sick guy met, they know nothing about location. So how shall they filter it?
The only significant effect of such an app is to keep focus on social distancing. Don't forget it, or you might be caught redhanded by the app. I manage to stay at a reasonably safe distance even without an app!
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Sounds like you're saying that if the solution doesn't work 100% (or even 80%) it's not worth it.
I respectfully disagree. If there is an agreed goal to isolate infections as fast as possible then even incremental solutions are better than throwing up your hands.
We're a clever bunch, with most cleverer than I. I reckon there's plenty of scope here to come up with something that works well enough and protects privacy.
cheers
Chris Maunder
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I am saying that if it works for (significantly) less than 10% of the cases, it is a waste. At a significant cost. I don't think the very minor benefit is anywhere close to worthwhile for the cost.
I am not talking about economic cost. We are accepting an ever-increasing level of monitoring and tracking. Don't forget that you "secret" ID is continuously broadcast as long as the app is running. Any surveillance camera picking up your face, along with the ID you broadcast, will know that whenever that ID is detected, it is you.
In Norway, a couple years ago, one of the government parties tried to force through a law permitting the police to infect any Internet PC with spyware, such as a keylogger, saving every keystroke you make. It didn't go through the parliament, and today that party is out of the government. But it might come back, stronger, and may force their old proposal through. If police is allowed to infect your PC with a keylogger, that isn't far from being allowed to infect your phone with a location logger.
Tracking by the GSM signals - the phone regularly announcing its presence to all base stations in the area - has been available for low-resolution tracking since GSM's arrival. In a kidnapping case ten years ago, police proudly stood up in media and explained how they "by a simple keypress" can trace every single mobile phone in the country: They could trace the movements of the victim's phone and follow the kidnappers. Unfortunately, they were to late to save the victim (see Murder of Faiza Ashraf - Wikipedia[^]), but after that, there has been full acceptance for police tracking by GSM signals: See - police can use it to track criminals! That's great isn't it?
If police infects our mobiles with a location tracker, after a single case where they have (say) identified drug distributors by tracking who the street dealers are in contact with, there will be no opposition to the exact tracking of anyone, so police can identify every single person you are near for more than a few seconds, whenever they think knowing your personal contacts can tell them something that they want to know.
The Norwegian app use not only Bluetooth to estimate the distance between persons, but also GPS, to identify the environment where the encounter took place: On the street? In a grocery store? At a sports event? - I can easily understand that this provides the researchers with a lot of valuable information about how virus spreads. The implication is that the authorities know everything about where I move, at all times, as long as I have the phone in my pocket.
I am not paranoid by the corona app in itself. The government has made regulations saying explicitly that the police shall not have access to the data base. (The regulations also state explicitly that the government can change the regulations at any time.) But this app serves as a prototype for perfecting this technology, under a cover of "this is to everybody's best". There is nothing to keep the police from drawing on the experience gained, when they will improve the precision of GSM tracing to that of GPS, augmented by Bluetooth for identifying social contacts. Once the corona app is accepted, that kind of police operations will be fully accepted (like GSM after that Faiza case).
In Norway, we had some general restrictions on traveling, and some people were in quarantine. Lots of people broke those restrictions; maybe they should all be put in jail, based on police tracking. GPS tracking allows police to identify every car that moves above the speed limit; maybe all those drivers should be fined (or more). Police knows of the activities of people illegally distilling alcohol; maybe, when rumors tell that he has readied a new batch, everybody who visits his house for five minutes the next couple of evenings should be called in by the police for interrogation. If a pedestrian is found in the ditch along the highway late at night, hit by a car, and the GSM logs show that you were the only one driving on that road around the time of the accident, you might have to hire a lawyer.
Pick your choice: If police can trace every individual, they can trace every criminal and catch them. They can also track lots of tiny law breaks by you, such as speeding, or going outside of city limits when it is strictly not legal. You might be accused of criminal actions, on the simple ground that you were the area at the wrong time.
Or, you might say that your privacy, your right to move around without being continuously traced (even "potentially" although it doesn't happen all the time) is so valuable that you are willing to let criminals be caught by traditional measures, even if one or two of them might get away. Fighting criminals is not the only value we fight for!
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I am not saying "over my dead body". I had an iPhone for many years and currently use a not rooted Android smart phone.
I partially agree with you in your first paragraph.
But in the second...
Chris Maunder wrote: I think Google / Apple have discussed this one ...
...
...
That's it. Start to end. You can delete the app. You can wipe any trace of the ID from your phone. The ID was never associated with you in any way. There is NO GPS logging.
Anyone see any holes in this?
Apart from "Google / Apple" and "The ID was never associated with you in any way." in such a little text? Seriously?
Several years and many articles / reports confirm that is a bit of an oximoron.
M.D.V. 
If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about?
Help me to understand what I'm saying, and I'll explain it better to you
Rating helpful answers is nice, but saying thanks can be even nicer.
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Let me clarify:
Google/Apple (I think) have discussed the "use bluetooth to detect proximity". I wasn't suggesting we use a Google/Apple app.
I actually also said such an app is actually not even needed - they already track us really, really well. (sure, not indoors, and not to within 6 ft, but track us enough to know that I was standing inline outside the grocery store that had 2 positive cases in that same line)
I think of this purely as a technical issue. The political, social, epidemiological issues merely complicate the process. Much like users. <shudder>
cheers
Chris Maunder
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Chris Maunder wrote: Google/Apple (I think) have discussed the "use bluetooth to detect proximity". I wasn't suggesting we use a Google/Apple app.
Sorry if I miss-read something.
Chris Maunder wrote: actually also said such an app is actually not even needed - they already track us really, really well. (sure, not indoors, and not to within 6 ft, but track us enough to know that I was standing inline outside the grocery store that had 2 positive cases in that same line)
exactly. Although I am not really that positive that even that would help that much. As Member79xxx said, it only might work (no certainty at all) if everyone is carrying a working smart phone.
If not... I think it can do more harm than help.
People starting to have symptoms that check the app and see "no potential contact registered" are going to think... "oh, ok, I haven't been exposed, so it is not CV" and this thinking is going to make them even more dangerous.
I think it is like with autonomous driving, it will only work, once ALL the cars are autonomous. As long as there is a mix on the road, forget it, the number of accidents will ramp up like hell.
For me the best protection we can use is just to switch our brains on, be careful without panicing and pay attention to what we do.
M.D.V.
If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about?
Help me to understand what I'm saying, and I'll explain it better to you
Rating helpful answers is nice, but saying thanks can be even nicer.
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Nelek wrote: the best protection we can use is just to switch our brains on,
Whoa, whoa, WHOA.
Now you're just talkin' crazy.
cheers
Chris Maunder
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Looking at the news and how people was behaving...
It was not that obvious 
M.D.V. 
If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about?
Help me to understand what I'm saying, and I'll explain it better to you
Rating helpful answers is nice, but saying thanks can be even nicer.
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The problem isn't in your approach. The problem is that whatever solutions are created will include unnecessary features and data handling that lend themselves to misuse.
Normally I'm an optimist, but the Wild West of mobile app development does not give me confidence.
Software Zen: delete this;
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Gary R. Wheeler wrote: include unnecessary features
Sounds like you are saying someone could create a framework for this.
My plan is to live forever ... so far so good
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It's a combination of YAGNI (You Ain't Gonna Need It) and "since we're here, and we've got 'this', let's record 'that' too". There's a tendency in any kind of data acquisition application to record everything possible.
Software Zen: delete this;
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Should you be alerted if you came into contact with someone that came into contact with a confirmed case, i.e. 2nd-hand contact (or even 3rd-hand contact)? If so, then all your close-encounter data needs to be harvested, which removes the veil of security in the original proposal.
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I tend to agree with you, @chris-maunder - it's obvious that 'standard' contact tracing mechanisms don't work with something as infective as covid-19 and if we don't want one of extended lockdown or health system overload, we as societies (whichever one we happen to live in) need to change things about how we operate, whether that be apps like this or/and wearing masks full time (as happened in places in North America after the flu of 1918/19 - it only lasted a year or so, though, until masks were discarded). And having had first and second hand experience of covid-19, ICUs and ventilators, I can say I don't want people to have to go through all that if it can be avoided.
At the same time, I understand the reluctance to trust organisations like governments or commercial entities like Google and Apple. I know their interests and desires aren't going to be aligned with mine (except through occasional lucky coincidence), but I think this is one area where they might be pulling the same way...
Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p
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I don't like giving companies the meta-data to do contact-tracing, because the market is quickly pivoting to make huge profits off of the technology, with a strong disregard for the mid-term consequences.
It's not even the privacy concerns I'm worried about, I'm only worried about enabling governments to identify dissidents in a novel way. What if it gets used to contact-trace minorities? You could, in theory, identify and target any minority; information that can be used to push almost any political agenda.
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Yeah...I see holes....
Let's start with #1.
The "only on your device" is something you won't know. They also said you can recreate your GUID so that means the police can recreate your GUID.
Then...when you get diagnosed as a COVD carrier and you smoosh the button...who's to say your phone won't scream at every other phone in the office...or the 120 kids are in your class...? Let's shut down businesses!! When this "6 foot" rule is being incorrectly applied as a cure all.
The 6 foot rule came from an study on airplanes of "how close is too close" and they found that less than 6 feet for more than 10 minutes was too close. They didn't come up with any graphs that showed that 7 feet for 12 minutes is safe. They are finally starting to figure out now that all you have to do is walk through an area where an infected person has breathed and you can get it. No sneezing or coughing needed. It sounds like COVD has a very high replication rate so even a small viral load can overwhelm your antibody production.
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Using the app is not the problem.
Someone can build a simple scanner that records all GUIDs in a given area.
Link that say, to a camera and now you have a face with the GUID.
The next time you see that GUID, you can look for a face.
That GUID is specific to a phone/person.
Remember the WiFi trash cans in London ?
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Well, to get back to the original subject/proposal;
Anyone see any holes in this?
One of the big problems I see, is that BT is also working through glass and through plexiglass screens. So the "near for 15 mins" parameter should somehow account for that.
I broke my head over this, the last couple of days, but couldn't come up with a solution. Anyone?
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Apparently the Australian tracking app doesn't track location, but they can't release the source code to prove it because "security reasons".
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That's not how security works... 
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I'd rather die as a free man than live forever as a slave.
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I'd prefer not to die at all 
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Actually, I've heard the Google plans to slipstream the tracking application as essentially an OS update.
Truth,
James
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... a 2020 planner!
Anything that is unrelated to elephants is irrelephant
Anonymous
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The problem with quotes on the internet is that you can never tell if they're genuine
Winston Churchill, 1944
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Never argue with a fool. Onlookers may not be able to tell the difference.
Mark Twain
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you can still plan your travels to the kitchen, etc.
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Nope. I'm banned from opening the fridge...
Anything that is unrelated to elephants is irrelephant
Anonymous
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The problem with quotes on the internet is that you can never tell if they're genuine
Winston Churchill, 1944
-
Never argue with a fool. Onlookers may not be able to tell the difference.
Mark Twain
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