My co-blogger David Post says that the Fourth Amendment allows air travelers to leave airport security screening areas if they wish without the TSA’s permission:

I am permitted to leave [the screening area] without TSA permission, whether they like it or not, because the Fourth Amendment’s prohibition on “unreasonable . . . seizures” gives me that permission. We have a word for this, too, in the law, when government agents don’t allow us to leave freely: ”being in custody.” And the government cannot put me in custody when they have absolutely no reason to believe that I have broken the law – the 4th Amendment prohibits that. Nor can they say “you’ve consented to being in custody when you go to the airport,” any more than they can say “you’ve consented to being in custody whenever you leave your home, so we can grab you and hold you whenever we damn please.”

It’s perhaps worth noting that the caselaw is generally to the contrary. The “right to leave” argument was first litigated in the early 1970s when airport security screening was new. At the time, the Fifth Circuit clearly rejected the argument. See United States v. Skipwith, 482 F.2d 1272, 1277 (5th Cir. 1973). The Fifth Circuit reasoned that an alternative approach would give hijackers a way to probe for poor security practices and then only go through security when it was lax:

[A right to leave the screening area] greatly damages the prophylactic purpose of the search procedure. Such an option would constitute a one-way street for the benefit of a party planning airplane mischief, since there is no guarantee that if he were allowed to leave he might not return and be more successful. Of greater importance, the very fact that a safe exit is available if apprehension is threatened, would, by diminishing the risk, encourage attempts. Established search procedures are perhaps more valuable by what they discourage than by what they discover. I see no constitutional requirement, where a defendant knew by objective signs that he was incurring the possibility of a search, that he should thereafter be allowed to play heads-I-win, tails-you-lose.

Eleventh Circuit later justified this result on grounds of consent, contra David’s view: “[T]hose presenting themselves at a security checkpoint thereby consent automatically to a search, and may not revoke that consent if the authorities elect to conduct a search.” United States v. Herzbrun, 723 F.2d 773, 776 (11th Cir. 1984). I take the idea to be one of consent, not custody. A passenger can’t leave because that would revoke consent.

In the 1970s, a string of cases from the Ninth Circuit suggested more sympathy to the right-to-leave argument. See, e.g., United States v. Davis, 482 F.2d 893 (9th Cir. 1973). But the Ninth Circuit eventually rejected those precedents and aligned its views with the Fifth Circuit, albeit applying the “special needs” doctrine instead of consent:

[R]equiring that a potential passenger be allowed to revoke consent to an ongoing airport security search makes little sense in a post-9/11 world. Such a rule would afford terrorists multiple opportunities to attempt to penetrate airport security by “electing not to fly” on the cusp of detection until a vulnerable portal is found. This rule would also allow terrorists a low-cost method of detecting systematic vulnerabilities in airport security, knowledge that could be extremely valuable in planning future attacks.

United States v. Aukai, 497 F.3d 955, 960-61 (9th Cir. 2007) (en banc).

One area of potential ambiguity is identifying the exact point that passengers lose their right to leave. The Ninth Circuit was deliberately unclear on this in Aukai. As I read Aukai, the right is lost when the passenger attempts to enter the “secured area” of the airport, with the catch that the “secured area” is not readily defined:

The secured area includes the “sterile area,” which “means [the] portion of an airport defined in the [TSA] airport security program that provides passengers access to boarding aircraft and to which the access generally is controlled by TSA … through the screening of persons and property.” Id. Because of security concerns, the Government has not made public the details of “airport security programs.” See 49 U.S.C. § 114(s); 49 C.F.R. § 1520.5. Hence, we do not speculate on how far such “sterile” and “secured” areas extend from the airplane boarding gate to the street door.

Id. at 961 n.8. This point is clearly triggered by the time a passenger places her luggage on the conveyor belt for inspection, see id., but I take Aukai to leave open the question of whether the right to leave is lost by the time the passenger presents her ID and ticket for inspection before entering the screening area. There may be some cases on that, but my quick skim didn’t uncover it.

Anyway, that’s my best sense of the cases. I recognize that some readers will contend that the cases are irrelevant to what the law truly is. If the cases say that, they will reason, then it just shows how the judges don’t understand what the Constitution truly means. Perhaps. But at the very least, the appellate caselaw explains why the TSA thinks its policy is constitutional.