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The ACLU of Southern California filed a public records request today demanding more information about the body scanners that the Los Angeles Metropolitan Transportation Authority is deploying in subway stations purportedly to detect terrorists. There are a lot of unanswered questions about these body scanners, which see through clothing to detect objects on people鈥檚 bodies. These questions concern numerous privacy and racial equity issues 鈥� and ultimately, the question of whether we want remote body scanning to become pervasive in our public spaces.

We wrote about this technology and the questions it raises in March when TSA tested it in New York鈥檚 Pennsylvania station. The privacy questions include whether the scanner searches are permissible under the Constitution under California鈥檚 very privacy-protective state constitution without a warrant and whether an alarm by one of these scanners is sufficient to justify a demand by a security officer to see underneath a person鈥檚 clothes. People carry all kinds of personal effects on and about their bodies, especially in a busy place like a transit hub, and many of those things are very personal: valuables; back braces; medical devices, such as colostomy bags and prosthetics, etc. We should also bear in mind that this technology will likely improve over time in its resolution, clarity, and effective operating distance 鈥� and will, therefore, become more intrusive.

There are also serious questions about its effectiveness and whether it survives a cost-benefit analysis. We don鈥檛 know what the system鈥檚 false positive and false negative rates are, but with all of the things that people carry, it鈥檚 likely to be generating constant false alarms. For instance, a German study found a strikingly high false positive rate of 54 percent in the use of these scanners. In other words, more than one out of every two items tagged as suspicious turned out to be innocuous. And that was the version used in airports on subjects who are standing still with their arms raised and their pockets empty rather than the free-standing version used here on moving crowds in a chaotic environment. Similarly, the risks of the false negatives 鈥� the rate at which these devices fail to detect actual threats 鈥� are potentially astronomical as well. In 2017, the Department of Homeland Security's internal watchdog that its undercover agents were able to slip contraband through TSA鈥檚 suite of security screening protocols in over 70 percent of attempts.

We don鈥檛 have anything like sufficient information to suggest that these devices will be effective in preventing mass casualty attacks. The government hasn鈥檛 made the results of its tests in Penn Station or elsewhere public. And even if we did have cause to believe they鈥檇 be effective, remember that, as security experts have long pointed out, when you harden one target, attackers will simply shift to a softer target. That is especially true of terrorists, who generally don鈥檛 care about disabling or degrading a specific facility but are simply interested in creating publicity and terror.

More broadly, this development is the latest to threaten the 鈥渁irportization of American life.鈥� Under the Constitution鈥檚 Fourth Amendment, police officers and other government agents ordinarily can鈥檛 search you without a warrant supported by probable cause. The courts have accepted an 鈥渁dministrative exception鈥� to that requirement for the narrow purpose of detecting weapons and explosives that might be brought aboard aircraft. One of the questions raised by the Los Angeles body-scanner deployment is whether we鈥檙e going to allow that narrow exception to our privacy rights to be wedged wide open into a world where we are constantly searched as we circulate throughout our public places, effectively rendering the Constitution鈥檚 protections meaningless.

Los Angeles鈥� Union Station, for example, contains numerous restaurants, houses art exhibits, hosts weddings, and attracts tourists to view its renowned architectural elegance. New York鈥檚 Pennsylvania Station, where this technology was also tested, is similarly a contiguous part of New York City鈥檚 public spaces, with plentiful entrances and exits and numerous stores and restaurants. Neither are anything like the secured area of an airport. It鈥檚 hard to imagine that even with hundreds of body scanners installed throughout these stations, such scanning would be at all effective in detecting a sole bomber from among the 700,000 people who flow in and out of the two sprawling .

TSA Administrator David Pekoske reporters of the deployment, 鈥淲e will not have a repeat of 9/11 or any terrorist incident inside our transportation systems in the United States.鈥� As far as the Los Angeles subway goes that鈥檚 fairly certain because you can鈥檛 drive a subway train into a building. Mass transit facilities are far more like regular public spaces than they are like aircraft. Aircraft are uniquely structurally vulnerable to attack, uniquely terrifying to passengers contemplating such attacks, and uniquely able to be weaponized against ground targets.

Our domestic security bureaucracies will, like the Sorcerer鈥檚 Apprentice, mindlessly press forward with their task beyond any point of reasonableness. That is the nature of bureaucracies, which, as we have argued elsewhere, are best thought of as mindless organisms with certain common characteristics. They will carry out their task of stamping out any risk of attack, no matter how small, without regards to cost, proportion, or damage to other values.

The continued occurrence of mass shootings may also be taken up by our security bureaucracies as additional fuel for the construction of a 鈥渃heckpoint and search鈥� society. Officials at the launch of the Los Angeles scanners cited guns as another justification for these searches. But consider the for security checkpoints, metal detectors, randomized searches, and onerous backpack policies at schools in the wake of any school shooting. The security apparatus鈥� response to the epidemic of school shootings is to turn schools into fortified bunkers rather than to invest time and resources into student programming, school supplies, teachers, restorative justice, student support, and mental health care 鈥� all of which actually may stand a chance of preventing an attack.

Los Angeles Metro鈥檚 acquisition of scanners raises another troubling reality: racially biased policing. These devices only identify potential risks. The officers tasked with operating them follow up on alarms by determining whether an individual deserves additional scrutiny, questioning, or detention. As , the insertion of line-level discretion in policing introduces racial bias in enforcement decisions. The use of body scanners threatens to exacerbate these disparities. If an officer is unsure about whether to question an individual who may have a suspicious device, they will inevitably be more likely to do so if the person is a Black man than a white woman. Worse still, these scanners may provide officers with an 鈥渙bjective鈥� basis to carry out a racially pretextual stop that they might not otherwise feel legally entitled to do.

In short, for all the specific unanswered questions raised by the Los Angeles subway deployment, which we are trying to get answers to today, the big question is whether we are going to go down the road of subjecting Americans to remote automated searches at every turn. The security bureaucracies and device manufacturers will be pushing for it, but that鈥檚 not how Americans should have to live.