Let me start by noting that I'm not opposed to airport security, I believe some level of security is necessary and appropriate. I am not a lawyer, so this is not legal advice. However, I can do research. Let's begin by looking at the text of the 4th Amendment to the US Constitution so it's clear what rights we're talking about.
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
I found a paper written in 2008 by a law school student, which specifically examines the constitutionality of using the backscatter scanners for airport security screening. Excerpts from this paper. The paper contains full case citations, which I've omitted for clarity and brevity.
The Court stated that evaluation of airport searches should be conducted using standards related to “administrative” searches.
To be valid, administrative searches must meet the standard of reasonableness as required by the Fourth Amendment. To be reasonable, a passenger “screening search must be as limited in its intrusiveness as is consistent with satisfaction of the administrative need that justifies it.” Consequently, valid passenger screening searches at airports must acknowledge a person’s right to decide not to board an airplane and therefore not be subject to the search.
The Court suggested that airports make the options available to passengers approaching screening areas so obvious that someone who decides to board an airplane has consented to the screening. However, at the time the incident at issue occurred, in 1971, “[t]he nature and scope of airport searches were not then widely known.” Therefore, without clear notice of the choice to be screened or not board the airplane, attempting to board the airplane was not necessarily consent.
The Ninth Circuit [court, stated] that under Davis, screening procedures at airports must be reasonable to comply with the Fourth Amendment. “An airport screening search is reasonable if: (1) it is no more extensive or intensive than necessary, in light of current technology, to detect weapons or explosives; (2) it is confined in good faith to that purpose; and (3) passengers may avoid the search by electing not to fly.”
In it's report on the scanners, the GAO stated:
...it remains unclear whether the AIT would have detected the weapon used in the December 2009 incident....
The millimeter wave scanners do not reliably image low density materials such as powdered, liquid, or gel explosives. The backscatter scanners only penetrate about 1-2 mm into the skin, so they don't detect items concealed inside the body, or under folds or flaps of skin. Neither system can actually detect explosives, they merely image the shape and rely upon the operator to detect an "anomaly" in the image. USA Today published portions of a Q&A session they conducted with TSA chief John Pistole, in which he admits to those limitations.
Bomb sniffing dogs and electronic trace detectors, aka "sniffers" are far more effective at detecting explosives than are the scanners. Neither dogs nor electronic trace detectors involve invasive searches or pat downs. The FBI and military use explosive detecting dogs because they're more effective, cheaper, portable, and don't require someone to stop and pose for them to be effective.
Below are my conclusions:
So, we have expensive scanners, that don't reliably detect the very types of explosives and devices that have been used in the attempts that have been made since 9/11. These scanners effectively create and display a "nude picture" of the person scanned, which is clearly an invasion of privacy. These scanners do not make flying any safer than the prior screening process using metal detectors.
As the backscatter scanners are neither the least intensive nor most effective technologies currently available for the detection of weapons or explosives, the use of these scanners is in direct conflict with prior court findings and the established criteria for "reasonableness" for airport screening. Therefore, using these scanners as a primary screening device fails to meet the standard and is a violation of the 4th Amendment prohibition on unreasonable searches.
Furthermore, the nature and extent of what is visible to operators of the backscatter scanners and the nature and extent of the enhanced pat down procedures is not yet widely known, therefore, by the previous findings of the court, most passengers may not have consented. I assert that if the TSA where honest with people about how detailed the images are, and how invasive the pat downs are, most people would not consent. When informed of the fact that they don't make flying any safer, I believe very few would consent.
Note, that the author of the referenced paper studying the constitutionality of these scanners arrived at a similar conclusion. He/She notes that the backscatter scanners might pass the test if they're a secondary screening device. However, that point is moot now that the TSA has stated that they intend to use (and in fact are using) the new scanners as a primary screening device.
Burden of Proof:
Given that an "unreasonable search" without a warrant is prohibited by the 4th Amendment, any agency implementing an administrative search is requesting an exception to do something that is explicitly prohibited unless it falls within the strict requirements for an administrative search. That puts the burden of proving that a search (and methods/equipment used for a search) meets the explicit requirements to be classified as an administrative search upon the person/agency performing the search. Thus, the TSA must prove that these scanners meet the criteria set forth above. That they have not done so, and in fact have refused to provide any proof of their effectiveness as compared to less invasive and less intensive methods, means they have not met the criteria for an administrative search, and therefore, are in violation of the 4th Amendment prohibition against "unreasonable search".
The "Enhanced Pat Downs":
The new "en-hands-ed pat downs" as I prefer to call them, are also a gross violation. They feel you all over, including your genitals, butt, and breasts. They're more intensive than the police use when you're arrested, or when you're entering prison. They amount to being "groped" which is a type of sexual assault. That is not acceptable, it's not legal, and we can not allow it to continue.
These "pat downs" are being performed on people who haven't even been accused of a crime, much less arrested or convicted. They're being performed on children, teens, adults, senior citizens, etc. People in a wheelchair and those with many types of medical implants or prosthetics will always receive one of these "pat downs" either because they can't go through the detector/scanner, or because they will always trigger an alert on the detector/scanner.
There is nothing "reasonable" about groping passengers. There is no way this can be considered to pass the "reasonableness" test, given that it must be primary screening method for many people due to their use of medical devices.
This is not a "slippery slope" we're on, it's a steep hill of solid ice, with no way to get traction once you go over the edge. At the bottom of the hill are whips and shackles. We must demand that the government stop violating our rights.
But don’t take my word for it, research it yourself, all the legal citations are in the document I linked at the beginning. For another view, check out this op-ed piece in the Washington Post. It covers some of what I cover above, and it's from a law professor.
I believe it's possible to improve airport security without invading our privacy or violating our rights. There are less invasive, less expensive, and more effective ways to implement airport security. We need to demand that they use legal, practical, sane, and effective security procedures, not these gross invasions of our privacy and illegal searches of our persons. I'll detail some of those methods in my next blog post.
Update 2010-12-08 @ 17:15
Updated to clarify that MMW scanners can't image low density materials and that neither type of scanner actually detects anything, they require an operator to notice anomalous shapes.
Update 2011-07-21 @ 12:15
Added section on burden of proof.