An acceptable false negative rate really depends on the consequences of getting caught.

If someone's nefarious plan depends on smuggling a gun in, they want to be confident they won't be arrested or shot at the entrance. Even failing to detect 20% of firearms means there's an 80% chance they'll be caught before they can do whatever it is they plan on doing. This is also why it's important to have armed guards alongside the scanners. Scanners aren't very useful if the only armed person is the bad guy.

If the consequences of getting caught are negligible (as is the case for anyone trying to bring a box cutter through airport security), then the attacker can try as many times as they want without issue. Even if the false negative rate is low, they only have to get lucky once.

Annoyingly, I can't find any info about false positive/negative rates for various scanners. There doesn't seem to be the equivalent of Consumer Reports or Underwriters Labs for scanners. My guess is that the numbers must be pretty bad if companies aren't willing to go through public 3rd party testing.

The TSA's own security tests clearly show a significant percentage of guns, knives and explosives regularly get through. This is further confirmed by the number of travelers who, after arriving, discover the handgun they accidentally left in some pouch in their suitcase that was never detected.

> There doesn't seem to be the equivalent of Consumer Reports or Underwriters Labs for scanners. My guess is that the numbers must be pretty bad if companies aren't willing to go through public 3rd party testing.

Of course they are but the main reason there's no publicly available objective testing isn't only that sellers don't want it. In reality, no stakeholder in the security market wants it. The vast majority of high-volume public security like airports, concerts and sporting events is largely unnecessary and mostly ineffective but our current political/media environment requires appearing to "do something" to "make it safe". The Vice-President of "Make it (Seem) Safe" knows that their shareholders, politicians and the public aren't willing to pay more or be even more inconvenienced than they already are for 800% better "Make it (Seem) Safe"-ness.

Metaphorically speaking, the tiger repellent is working just fine, thank you. Those truly worried about tiger attacks feel safer and those being well-paid for preventing tiger attacks can claim virtually 100% effectiveness. So, if you start the world's best Tiger Repellent Testing Laboratory, you'll find a shocking lack of interest in buying your test data from both sellers and buyers in this brisk, profitable and growing market. Much like the lack of interest in objective testing data for lie detectors, astrology readings and placebo pills. The smaller minority of customers actually willing to pay more for improved detection (like Tel Aviv airport), do their own in-context performance testing anyway. In fact, a good proxy for doing your own effectiveness testing is available for free. Just look at what those under constant active threat with real consequences actually pay for and do.

I unknowingly transported ammo both to and from Mexico. I used an old backpack that I had previously used as a range bag from years ago. I ended up finding several 223 rounds in Mexico, then when I got back, even more 22lr.

Others have not been so lucky

https://www.independent.co.uk/news/world/americas/kyle-busch...

Failing to detect 20% of firearms is probably a really deal. I would bet the majority of findings are just ordinary people who forgot to leave their gun in the car (akin to how TSA used to take grandma's knitting needles away every flight).

So, if your process really only detects people not trying to bypass it and people not even in the wrong then it's a problem.

Although I mean with the long lines at security you might as well just gun everybody down outside the stadium in that nice open area they are all packed into ...

> Security checkpoints are the primary point of delay for getting into venues, and places that have rolled these out process people through about 95% faster. It's a huge difference.

I assume expediting peak crowd throughput at low labor cost is the primary, if not entire, value of the device. I hate that it's being marketed dishonestly but I also assume most concert venue buyers know (or suspect) it probably doesn't work all that well in practice. However, in a concert context accurate detection isn't their main priority. They need to get more bodies per minute into the venue at lower cost while appearing to conduct security checks sufficiently 'real' enough to act as a deterrent to get those who care about getting 'caught' to leave their knife or concealed carry handgun (or whatever) in the car.

The only hard and fast requirement is meeting the contractual security requirements of the venue and promoter's insurance carriers - because no insurance = no concert. It's a bonus if the 'security' also looks plausible enough to reassure the small fraction of perpetually fearful people statistically challenged enough to actually worry about terrorists or an active shooter killing them while at a Taylor Swift concert (as opposed to the infinitely more likely chance of dying in a car crash on the way to the concert).

In a perfect world, everyone would be rational and numerate enough that we wouldn't need to maintain the pretense of 'security theater' in contexts where actual security isn't necessary. But in the imperfect world we live in, I prefer having concert (and airport) security be as minimally disruptive and inexpensive as possible regardless of effectiveness (since it's unnecessary and mostly ineffective in those contexts anyway). I just wish companies would sell these products as 'security placebos' instead of lying about it because fraud is wrong.

I don't know anything about the devices that are being sold, but it doesn't seem impossible to me that with better signal processing from a metal detector, you could reduce false positives a bit while maintaining or slightly improving the false negative rate.

Sure, I agree that's an interesting and likely solvable technical problem. However, the vast majority of the addressable market in today's over-secured society don't really need improved detection. Concert venues, sports arenas and similar customers buy massive volume and they are much more concerned with faster throughput enabled by shorter cycle time and minimal false positives. Of course the head of security at Madison Square Garden can never publicly admit they don't care about better detection enough to pay more for it, but I'm confident the sales managers at these security vendors understand exactly what their largest market segments really care about.

Customers like Tel Aviv International Airport, who actually care to some meaningful extent about improved detection, are a small minority segment of the overall market. Creating new technical measures able to demonstrate improved performance in rigorous objective tests on the metrics these customers care about (some sweeter spot on the matrix of false pos, false neg, true pos, true neg, net throughput, cost) would be valuable but only to that small segment.

Note that I said lower false positives and equal or slightly better false negatives, which aligns with what you say customers want.

Of course I suspect venues really don't care about false negative rates much at all, so there's a big temptation for everyone to just turn sensitivity down.

Very likely, but who's going to pay for the engineering efforts? If the customer doesn't care about having a better device, or a better device would actually make their job harder, then it's wasted effort on the part of the manufacturer.

Engineering exists to solve a problem. It's entirely likely that your definition of the "problem" differs from that of the paying customer.

> get more bodies per minute into the venue at lower cost while appearing to conduct security checks sufficiently 'real' enough to act as a deterrent

Or they just need to convince most of their customers it will be safe to attend, while covering their ass by following "best practices" if something slips through, people get hurt and they get sued.

> convince most of their customers it will be safe to attend

Apparently, you've never met my Aunt Sue. She has a graduate degree in innumeracy with a minor in illiteracy and a specialization in worrying about whatever the media tells her to worry about. However, she always votes.

More seriously, it's not cost-effective to "convince most customers it will be safe enough to attend." The game theory around fallacious public perception makes it a losing proposition for a politician or company to ever be seen as reducing security requirements because as soon as "rare bad thing happens", you will be blamed - even though your reduction in pointless measures had no bearing on it. Every independent expert agrees that securing cockpit doors makes subjecting every passenger to the TSA's increased security measures unnecessary and, objectively, a very poor ROI in both cost and disruption. However, the TSA will never, ever go away - even though it could and should. Yes, this is frustrating.

They don't need to convince most of the public, just enough so they can fill up their venue. There are some Aunt Sues who are too afraid to go to concerts, but concert venues are still able to fill up when they have a popular act so it stands to reason that they're managing public perception of the risk well enough for their own needs.

> The only hard and fast requirement is meeting the contractual security requirements of the venue and promoter's insurance carriers

I think it would be a good idea to create an explicit carve out in the law saying that there is no premise liability for a property owner or event organizer due to a third party committing a crime.

So, do away with all negligent security cases?

Yes. In general, business owners aren't expected to prevent crimes against their customers. If someone attacks me at a bar or grocery store, I probably won't get very far trying to sue the owner for failing to check everyone for weapons on entry. I'm not sure I'd have more success with a concert venue, but it appears insurance companies perceive enough risk to demand certain procedures.

Codifying that expectation in law would reduce costly and obnoxious security theater. Of course, a business advertising a certain level of security could be sued for failing to provide it.

Ok, but it seems like a bit of a non-sequitur to say “ business owners aren't expected to prevent crimes against their customers” when there’s a body of law to the contrary.

Is there? In most US states, the concept of premises liability seems to be derived entirely from case law, not statute. Some states appear to have statutes limiting its scope, such as https://colorado.public.law/statutes/crs_13-21-115

Edit: to be clear, I don't think there's anything actually stopping someone from attempting to sue a bar or grocery store over a crime committed there, but it usually doesn't happen and would likely be an uphill battle for the plaintiff.

So what? It's not like common law has less effect. "Body of law" is understood by lawyers to include both common and statutory law.

I will concede the technical point: there is a body of law that sometimes expects business owners to prevent crimes and sometimes doesn't, with a whole lot of ambiguity about exactly what any given owner is actually expected to do. I think that ambiguity should be reduced by putting criminal acts out of scope.

The point is that it can easily be overridden with statute

"business owners meeting definition X are only liable in conditions Y"

This is a stupid point. “The current law can easily be overridden by passing a new law.”

No shit.

I think a better argument here is that common law/case law here is ambiguous enough to create a situation where there's an unreasonable and unpredictable risk for certain kinds of businesses.

Another problematic case this sort of liability leads to is hotels in Las Vegas routinely searching guest rooms after a lawsuit following the 2017 shooting. I don't think it's desirable to expect hotels to search rooms or to call the police if someone has "too much" luggage. That's paranoid, an invasion of privacy, and unlikely to prevent a future mass murder.

I don't want a world where I have to submit to searches to go anywhere or do anything, and I hope that's not a fringe position.

I was only responding to GP's statement that common law can be overridden by statute.

If I wanted to respond to the idea that premises liability should be eliminated then I would have responded to your first post.

And I actually do think that most people would call your position a fringe position once you actually start talking details like "but what about guns in schools?" If you truly believe that you shouldn't have to submit to a search to go ANYWHERE or do ANYTHING then you hold a fringe position.

My position is that it is undesirable for premises liability to lead to an increase in private businesses searching their guests, not that nobody should be searched anywhere for any reason. I do think it should be rare in practice: airports, probably; concerts, probably not absent some unusual threat; hotel rooms pretty much never.

It appears routinely searching students in public schools is fairly rare in the USA; under 8% use metal detectors[0]. That certainly does not mean they're allowed to bring guns, just that they probably won't be discovered if they do.

[0] https://nces.ed.gov/fastfacts/display.asp?id=334

No, your position is: "I think it would be a good idea to create an explicit carve out in the law saying that there is no premise liability for a property owner or event organizer due to a third party committing a crime." and "I don't want a world where I have to submit to searches to go anywhere or do anything."

This means that nobody should be searched when they go anywhere or do anything, and if they aren't and someone gets shot by a third party, stabbed by a third party, or mugged by a third party then there is no liability to the business/landowner in any case. Ever. Searches will not be rare in practice, they will not occur. Airports? Never. Concerts? Never. Hotel rooms? Never. Schools? Never.

And hence we've already established the problem with your position and why it's fringe. Not even you can realistically argue for your own positions without caveats.

I see the miscommunication now. It's possible to interpret what I wrote as "no places/activities should require searches", but what I meant was "not all places/activities should require searches". That's a bit hyperbolic of course since the resources don't exist to search everyone, everywhere, all the time. There has been an increase in recent years, and I would like it reversed.

I am opposed to premises liability being a motivation for anyone to conduct searches. Liability isn't the reason searches are conducted at airports or courthouses to give a couple examples, so eliminating it would not eliminate those searches. Businesses also might have other motivations, such as making their customers feel safer; if that outweighs customers finding it annoying or offensive, some of those would likely continue.

> someone gets shot by a third party, stabbed by a third party, or mugged by a third party then there is no liability to the business/landowner in any case. Ever.

This does correctly state my position.

You say that as if statues are any less ambiguous.

Theme parks are switching to these too and it's oh so much nicer to just walk through and if you're unlucky having your bag searched.

>TSA isn't great on their false positive rate, does more intense screening, and isn't being staffed by hungover 20-somethings. So maybe the false negative rate didn't actually increase by much?

TSA is abysmal on the false negative rate for things that actually matter. The FNR for actual weapons and explosives is somewhere between 80 and 95%[1]. It's because they waste all of their attention looking for nail clippers and water bottles.

Even an FNR of 50% would be a massive improvement.

[1] https://abcnews.go.com/US/tsa-fails-tests-latest-undercover-...

I guess on a more general level, I'm confused why a metal detector with bit some machine learning on top wouldn't make a better widget? You'd think that different shape metal object produce different magnetic flux, and there's probably more dimensions to that than just size?

If it's just a gate that you are walking through then it's all or nothing. Basically just a metal detector.

If you have a conveyor belt system and a CT scanner like setup then yes, you could build a better metal detector.