Any particular individual's movements could be tracked in the 1700s, and people have been tailed since forever. Your movements are in public space, no warrant was ever needed for that.
The judge was saying that the police needed probable cause and a warrant to search the Flock system because it's dragnet surveillance, similar to needing a warrant to access cell phone location data. [1]
Just because you don't have an expectation of privacy while moving in a public space doesn't mean you don't have an expectation of privacy for all of your movements ever in every public space. That scenario wasn't possible in the 1700s.
For an individual today, it's fine for the government to tail someone without a warrant. [2] It's probably not fine for the government to put a long-term GPS tracker on your car without a warrant (probably because the issue was sidestepped with trespass). [3]
Even Alito notes that in the past it would have required too much labor for the government to surveil every movement of an individual for a long period of time and so society has the expectation that the government is not doing that. [4]
[1] https://en.wikipedia.org/wiki/Chatrie_v._United_States
[2] https://en.wikipedia.org/wiki/United_States_v._Knotts
[3] https://en.wikipedia.org/wiki/United_States_v._Jones_(2012)
[4] https://www.law.cornell.edu/supct/pdf/10-1259.pdf#page=33
The expectation that the government doesn't tail everyone might have been reasonable, the expectation that the government doesn't tail you without a court-approved excuse is not.
I'm not arguing there shouldn't be protection against total surveillance, I'm arguing the US constitution doesn't offer such protection.
Luckily, the courts disagree with you, and have for -probably- longer than you've been alive. From printed page 31 of [0], discussion of the Constutionality of putting a radio transmitter in cargo in someone's car and tracking it:
But the defendant in that case raised concerns that “the result of the [Court’s] holding sought by the government would be that ‘twenty-four hour surveillance of any citizen of this country will be possible, without judicial knowledge or supervision.’” Id. at 283 (citing Br. For Resp., at 9). The Court addressed the defendant’s concern:
But the fact is that the “reality hardly suggests abuse[;]” if such dragnet type law enforcement practices as respondent envisions should eventually occur, there will be time enough then to determine whether different constitutional principles may be applicable. Insofar as respondent’s complaint appears to be simply that scientific devices such as the beeper enabled the police to be more effective in detecting crime, it simply has no constitutional foundation. We have never equated police efficiency with unconstitutionality, and we decline to do so now.
Id. at 283–84 (cleaned up).
More than 40 years have passed since the Supreme Court’s decision in Knotts, and this Court is now faced with technology that appears to be approaching the dragnet type law enforcement practice Mr. Knotts warned of. Therefore, lower courts need to reexamine the result in Knotts as technology advances past the rudimentary beeper in that case. Adhering too strictly to the Supreme Court’s language in Knotts about a person’s reasonable expectation of privacy in “his movements from one place to another” risks ignoring the Fourth Amendment principles at stake.
The whole document is well worth reading if you have a free fifteen-to-thirty minutes.
[0] <https://storage.courtlistener.com/recap/gov.uscourts.oknd.76...>
Yes but there is an expectation that the government doesn't tail you at all times for your entire life with no warrant, right? Largely because in the past it was infeasible for the government to do so: it cost too much money and required too much manpower.
That's what Alito was arguing in Jones: people expect to be tailed sometimes but they don't expect to be tailed at all times for a whole month. And commentary suggests the Court would have had a similar opinion if they had not sidestepped the issue by leaning on trespass.
As Alito said, the question the Court has not decided (and didn't need to decide in that case) is where the line is drawn. When does tracking a vehicle become a search and enter 4th amendment territory and require a warrant? (He said surely before 4 weeks.)