As mobile phone technology advances, privacy concerns for individuals continue to grow as well. With the use of biometric data to unlock a smart phone—for example, facial recognition technology or thumbprint-scanning technology—how might that impact the legality of a search in which a police officer gains access to the phone by merely picking it up and pointing it toward the suspect’s face? Or attempting to compel a person to provide their biometric data via court order?

Importantly, under the Fourth Amendment, the United States Supreme Court has found two branching paths for determining the reasonableness for a warrantless search: (1) whether the search implicates a violation of a reasonable expectation of privacy for the individual,[1] or (2) whether the search is a physical intrusion upon a constitutionally-protected area with the intent to gather evidence.[2] If either of these tests are met, evidence is suppressed.

With warrantless cell phone searches, the case law generally focuses on the reasonable expectation of privacy in a cell phone. Specifically, in Riley v. California, the Court indicated that a person generally has a reasonable expectation of privacy in the contents of a cellphone and held that police may not search the contents of a cellphone during a search incident to arrest.[3] The Court noted that there is a high risk of police uncovering personal details not relevant to the particular alleged crime.[4] Additionally, the Court noted that data found in a phone is often stored off-site (i.e., online or in the cloud), and thus the search goes beyond what is physically present during the search.[5]

However, Riley may not be wholly applicable in other instances, such as where police have obtained a search warrant.[6] It is also worth noting that, while the underpinnings of Riley are still relevant today, it was decided six years ago; in terms of technology advancements, that might as well be 600 years. For example, courts will eventually need to address whether a person’s reasonable expectation of privacy generally in the contents of a phone stays effective after an individual’s decision to make use of biometric-unlocking of his phone.

Perhaps the government could include such evidence in a case by making use of another warrant exception, such as plain view. There, the government could argue that in a search incident to arrest (or otherwise a valid circumstance for a warrantless search), the phone is sitting in plain sight and—knowing the phone could be unlocked by anyone picking up the phone and aiming it at his face—the defendant impliedly waived any reasonable expectation of privacy because he left the phone in an area the public could access and he chose to set up his phone to unlock through biometric encryption.

However, in Arizona v. Hicks, the United State Supreme Court held that the plain view exception does not apply in circumstances where the police have to physically move something obstructing their view of the item allegedly placed in plain view.[7] In Hicks, the police moved a stereo to see its serial number to confirm the item was stolen.[8] Could the Hicks precedent also apply if police pick up a defendant’s phone and point it at a defendant to unlock the phone through biometric data?

In any event, law enforcement can always obtain a warrant to search a phone. Armed with a warrant, police are free to search the phone—if they can access the data stored inside. That is, if police are unable to proceed past the encryption of the phone, they cannot physically access the information in the phone. If data on a defendant’s phone is encrypted, police can ask the phone’s manufacturer to bypass the security requirement or they can, via court order, compel the individual to unlock the phone for them.

While asking the manufacturer to bypass the security requirement could lead to other legal issues,[9] law enforcement agencies likely do not need to wander down this path—they can probably compel the user to unlock the phone for them.

Some recent cases have indicated a willingness on the part of courts to order suspects to provide their biometric data to police to unlock a phone. Particularly, in United States v. Barrera, a federal case in Illinois, the district court required a defendant to unlock his phone for police, who had a valid warrant to search the contents of the phone, by using his thumbprint.[10] The district court held that “compelling an individual to scan their biometrics, and in particular their fingerprints, to unlock a smartphone device neither violates the Fourth nor Fifth Amendment.”[11] It reasoned that because the police had probable cause to search the phone and because the defendant turned the phone over to police, the government “demonstrated probable cause to compel Barrera to use his fingers and thumbs in an attempt to unlock the phone.”[12] The district court  also held that this compulsion did not violate the Fifth Amendment right against self-incrimination.[13] While the act of using his thumb to unlock his phone is certainly compulsory and potentially incriminating, the district court  found that it was not testimonial.[14] In particular, the district court  focused on the fact that the act of using a thumbprint to unlock a phone is similar to using a key and does not reveal the defendant’s thoughts. Thus, the district court concluded that programming the phone to unlock by using biometric data does not cause biometric data to become testimonial evidence.[15]

In United States v. Wright, a police officer forcibly held a cell phone up to a defendant’s face.[16] The district court held that the officer’s action violated the defendant’s Fifth Amendment right against self-incrimination because forcibly unlocking the phone by holding it up to the defendant’s face was testimonial.[17] In Wright, detectives were investigating the defendant for suspected possession of child pornography.[18] Law enforcement obtained a warrant to search the defendant’s electronic devices, but the detective who applied for the warrant intentionally left out relevant information that addressed the credibility of an informant who provided a tip.[19] The informant was the defendant’s roommate, and the detective intentionally left out the informant’s prior felony convictions for crimes involving dishonesty, as well as personal disagreements between the informant and the defendant.[20]

Ultimately, the district court found that the warrant was still valid because even if the intentionally omitted information were considered, the warrant as a whole still contained sufficient probable cause for a search of defendant’s electronic devices.[21] Law enforcement faced other problems in Wright, however, because during an interrogation, when the defendant invoked his right to counsel after being read his Miranda rights, detectives picked up his cell phone and held it up to the defendant’s face to forcibly unlock it.[22]

The district court found in Wright that the detectives’ act of holding the phone up to the defendant’s face violated the Fifth Amendment because it compelled testimonial evidence from the defendant.[23] The district court reached this conclusion by relying on a comparison between biometric data and fingerprinting or DNA swabs.[24] Specifically, the district court determined biometric unlocking is “functionally the same as a passcode, and because telling a law enforcement officer your passcode would be testimonial, so too must the compelled use of your biometric feature to unlock a device.”[25] Additionally, the district court concluded that unlocking a phone with biometric data essentially is “testimony that you have unlocked the phone before, and thus you have some level of control over the phone.”[26] The district court stated that the because possession was a necessary element of the suspected crime in that case—possession of child pornography—it became more compelling to find the use of biometric data to unlock a phone as testimonial.[27]

Additionally, the district court concluded that the officer’s action potentially violated the defendant’s Fourth Amendment right against unreasonable warrantless searches.[28] The district court reached this conclusion because the warrant at issue in Wright was not obtained until after the officers held the defendant’s phone up to his face.[29] While evidence from the phone was suppressed, officers had lawfully found evidence through the warrant on other devices; there was actually no incriminating evidence on the phone.[30] While the defendant hoped to have all evidence suppressed, the district court declined to do so, noting that exclusion of evidence requires more compelling circumstances than those presented in Wright.[31] This was primarily because the issue at hand was one of first impression for the district court, and there was no definitive statement from either the Ninth Circuit or the United States Supreme Court; thus, the law enforcement officers in that case could not be said to have knowledge that their actions were unconstitutional.[32]

As the district court in Wright pointed out, most of the other trial courts that have addressed the biometric issue have done so in the context of warrant applications to search the contents of cell phones.[33] Some trial courts have found the compelled unlocking of a phone with biometric data encryption to be testimonial,[34] some have found only certain types of biometric data are testimonial,[35] and others have found no compelled use of biometric unlocking to be testimonial.[36]

Ultimately, it seems clear that whether or not police obtain a warrant, there may be no definite guaranty of privacy in the contents of cell phones encrypted by biometric data. Until there is definitive guidance on both the Fourth and Fifth Amendment issues, defendants and the government will likely battle over the proper scope and execution of a warrant to search a phone, as well as whether compelling a defendant to provide his biometric data is testimonial in nature.

Jake Old is a third-year law student at Belmont University College of Law, where he serves as the Editor-in-Chief of the Belmont Criminal Law Journal and Chief Brief Writer for Belmont's National Moot Court Competition Team. Prior to law school, Old worked in the print journalism industry as a beat reporter for local newspapers, writing about crime and courts. He is originally from Murfreesboro, Tennessee, and graduated from Middle Tennessee State University with a Bachelor of Science in Journalism in 2012.

[1] See Katz v. United States, 389 U.S. 347 (1967). 
[2] See United States v. Jones, 565 U.S. 400 (2012).
[3] Riley v. California, 573 U.S. 373, 401-403 (2014).
[4] Id. at 394-97.
[5] Id. at 397.
[6] Id. at 403 (“Our answer to the question of what police must do before searching a cell phone seized incident to an arrest is accordingly simple—get a warrant.”).
[7] See Arizona v. Hicks, 480 U.S. 321 (1987).
[8] Id.
[9] For example, the Third Party Doctrine, in which individuals forfeit any reasonable expectation of privacy by conveying information to a third party, could apply in some instances. See Carpenter v. United States, 138 S. St. 2206 (2018) (holding the third party doctrine does not apply to historical cell site location data).
[10] United States v. Barrera, No. 19 CR 439, 2019 U.S. Dist. LEXIS 202935 (N.D. Ill. Nov. 22, 2019). 
[11] Id. at *1-*2.
[12] Id. at *6.
[13] Id. *24-*25.
[14] Id. at *7-*8.
[15] Barrera, U.S. Dist. LEXIS,. at *16, *20, *22.
[16] United States v. Wright, No. 3:19-cr-00012-MMD-WGC-1, 2020 U.S. Dist. LEXIS 1414 (D. Nev. Jan. 6, 2020).
[17] Id. at *24-*25.
[18] Id. at *1-*2.
[19] Id. at *4-*7.
[20] Id.
[21] Wright, U.S. Dist. LEXIS,  at *15-*16.
[22] Id. at *2.
[23] Id. at *25.
[24] Id. at *23-25.
[25] Id. at *24.
[26] Wright, U.S. Dist. LEXIS, at *24.
[27] Id.
[28] Id. at *27-28.
[29] Id. at *1-*2.
[30] Id. at *28-*29.
[31] Wright, U.S. Dist. LEXIS, at *27-*30.
[32] Id. at *28-*29.
[33] Id. at *23, n. 8.
[34] See In re Search of a Residence in Oakland, California, Case No. 19MJ70053KAW1JD, 2019 U.S. Dist. LEXIS 212879 (N.D. Cal. Dec. 10, 2019).
[35] See In re Application for a Search Warrant, 236 F. Supp. 3d 1066, 1073-74 (N.D. Ill. 2017).
[36] See Matter of Search of [Redacted] Washington, D.C., 317 F. Supp. 3d 523, 539 (D.D.C. 2018).