In March of this year, Robert Harrison had a cell phone with him while he was inside his home. Though he has kept and used a cell phone as long as any of us, this time, things were different.

Unbeknownst to Harrison, Baltimore police officers were secretly transmitting signals through the walls of his apartment—without a warrant—to track the location of the phone in his possession. An undercover police officer had planted the phone weeks before with another person, Derrick Smith, who police were trying to convince to agree to a fictitious murder-for-hire plot. The device police were using to track the phone is called a cell site simulator, or more commonly, a “stingray.” It mimics a traditional cell phone tower—like those used by AT&T and T-Mobile—to force not only a targeted cell phone, but all phones in its vicinity to send location and identification information back to the device.

Baltimore police tracked the phone to Harrison’s address. Police then looked up the names of residents living at the address, including Harrison’s, and cross-referenced those names with information related to Smith. Based on what they reportedly found, police suspected Harrison of being an accomplice to Smith.

The chain of inferences leading to Harrison all stem from his possession of a phone, which the police did not learn through a lawful search of his apartment with a probable cause warrant, but instead through the warrantless use of a device that tracks phones—in secret. As Harrison faces trial on serious criminal charges, the government wants to insulate its use of a stingray with layers of excessive secrecy and expansive legal arguments. And that’s where the ACLU has stepped in.

Last week, we filed an amicus brief in Harrison’s case supporting his motions to the court to compel the government to give him information on the stingray so that he may build his defense against its unlawful use, and to suppress any evidence that Baltimore police obtained through use of the stingray.

In our brief, we make three arguments:

1. The use of the stingray violated the Fourth Amendment.

The use was unconstitutional because the government did not obtain a warrant, which is required in any use of a stingray because of the invasive nature of the technology. We present facts about stingrays that are relevant to the court’s understanding of just how intrusive these devices are:

Stingrays broadcast signals that penetrate the walls of homes and other constitutionally protected spaces.

Stingrays can pinpoint an individual with extreme precision.

Stingrays can search information stored on phones.

Stingrays significantly affect the privacy of innocent third parties.

Stingrays can disrupt the ability of phones in the area to make calls.

Even if the government had obtained a warrant in Harrison’s case, its use of the stingray would still raise Fourth Amendment concerns. This is because the Framers of the Constitution expressed a “revulsion” against “general warrants,” which is what a warrant to use a stingray may amount to, considering that the device can collect information about potentially hundreds of innocent bystanders’ phones.

2. The government did not properly obtain authorization to use the stingray due to the government's failure to explain to the judge that it was going to use a stingray.

The application the police submitted to obtain a court order (which is not the same as a warrant) for authorization to use the stingray was invalid because the application in fact requested permission to use a pen register/trap and trace device, which records the phone numbers with which a particular phone communicates. Pen registers, which have been in use for decades, have significantly lesser surveillance capabilities than stingrays, which acquire location and identifying information from all phones in the area. We explain how the government is engaged in a pattern of misleading courts in its requests for authorization to use stingrays (see here and here). In Harrison’s case, had Baltimore police been more transparent to the court, the judge may have demanded further information before issuing the order, or denied the request altogether.

3. The government should be compelled to disclose information to the defense about its stingray use.

The government has argued that it has a “law enforcement privilege” to not disclose information on police tactics and strategy. First, we argue, the law enforcement privilege is irrelevant to this case because it only applies to certain police methods that are not at issue here. More importantly, there is already a wealth of public information available about stingrays, much of it disclosed by the government itself in city government meetings, public documents, and other forums. The government is seeking to keep information about stingrays secret, but the reality is that it let the cat out of the bag a long time ago.

The ACLU takes a strong position against the government’s attempts to use new technologies to side-step old rules. Every person in this country has a right against unreasonable search and seizure of their persons, effects, and homes under the Fourth Amendment. When Baltimore police unlawfully sent a signal to detect the phone in Harrison’s home, it also gathered information about all the phones in the area—any one of those phones could have been yours or mine. Stingrays or not, the government must follow the rules when it conducts law enforcement investigations. Keeping information about its use of new technologies secret from the courts endangers our right to be free from unreasonable government intrusion into our private lives.