With a relatively low COVID-19 infection rate, Singapore credits some of its success to disease surveillance measures, including the government’s cell phone tracking application TraceTogether. With Americans increasingly becoming more comfortable with cell phone surveillance to combat the novel coronavirus, would something like TraceTogether be legal in the United States?

TraceTogether does not record location data, nor is information actively sent to the government. Rather, TraceTogether records which phones a given phone comes into contact with. The application sends out Bluetooth signals to nearby TraceTogether users and records any contacts on the phone itself. The data is encrypted and anonymized, meaning the data read as plain text cannot be connected to a specific individual. If a specific individual is a confirmed carrier of COVID-19, the government can request the person to upload his data. After three weeks, if there is no COVID-19 contact, the data is purged.

But could the government require a similar application in the United States or would it be a violation of the Fourth  Amendment’s guarantee against “unreasonable searches?” Generally, the Fourth Amendment may be invoked when a search infringes on a reasonable expectation of privacy, or the government’s activity amounts to a trespass, per the Supreme Court’s holding in Katz v. United States (1967) and United States v. Jones (2012).

The third-party doctrine complicates the issue as it can carve out exceptions to when a warrant is required to legally conduct a search under the Fourth Amendment. The doctrine applies when individuals voluntarily give information to a third party and the government gets information from the third party (e.g. phone records from a telephone company). In the landmark case Carpenter v. United States (2017), the Supreme Court declined to apply the third-party doctrine to the warrantless retracing of a cell phone’s location based on the phone’s connectivity with cell towers. This made the government’s search a constitutional violation because there was a reasonable expectation of privacy, seemingly implying that the government cannot simply track the location of individual cell phones.

However, under the third-party doctrine, it is unclear if the government could simply compel phone service companies to turn over data. If there is no individual suspicion that an individual is infectious or is in violation of a quarantine order, there could be a serious Constitutional challenge.

Apple and Google are planning to do something similar to the TraceTogether application and grant access to public health officials. Because their proposal requires people to voluntarily “opt-in”, it is unlikely that there would be a problem under a Fourth Amendment theory. If the government were instead to require Americans to install a tracking application on their phone, that would likely be construed as a government trespass, making it unconstitutional.

Further complicating the issue, warrants are not always required, such as when police are trying to prevent an imminent destruction of evidence, or when obtaining a warrant is infeasible due to exigent circumstances. During emergencies, the government is frequently afforded more legal leeway by the courts. If there is no location data, some legal holdings on phone surveillance may not apply, such as in the Carpenter case. Depending on the circumstances, the Fourth Amendment may not apply at all, though it is doubtful that an application that sends personal health information as an alternative form of data to the government, such as in the case of some measures in China, would comply with HIPPA privacy rules.

For these reasons it is imperative to approach the issue with caution and lawmakers should consider the sensitivity of the information on smartphones. As I have written previously, courts have not done well in adapting to new technologies. Though the intention to protect the public is noble, civil liberties should be preserved against surveillance state mission creep.