In this Nov. 27, 2017 photo, a communication technician works on a cell tower in Harrisonburg, Va. (Daniel Lin/Daily News-Record via AP)

HOW MUCH information about you is on your cellphone? Likely the most intimate details of your life: photographs, Internet searches, text and email conversations with friends and colleagues. And though you might not know it, your phone is constantly creating a record of where you are at any given moment through communications with your wireless service provider.

That record helped convict Timothy Carpenter, who received a lengthy prison sentence for his role in a string of burglaries in 2010 and 2011. Without a warrant, law enforcement officials reviewed more than four months of location records from Mr. Carpenter's phone and placed him at the crime scenes. The Supreme Court is now considering his story in what has the potential to be the court's most significant Fourth Amendment case in decades.

The American Civil Liberties Union argued before the justices that police should need a warrant before collecting cell-site location information over long periods. The ACLU is seeking to overturn the lower courts’ rulings against Mr. Carpenter, finding that the location records aren’t protected by the Fourth Amendment’s warrant requirement. Under the “third-party doctrine,” people give up their expectation of privacy when they share information voluntarily with a third party — like a wireless service provider. So instead of requesting a warrant based on the Fourth Amendment’s high “probable cause” standard, law enforcement was able to obtain records of Mr. Carpenter’s location after satisfying the lower standard of evidence federal legislation requires.

Congress passed that law in 1986 — before cellphones existed in their current form. Likewise, courts developed the third-party doctrine in the 1960s and '70s. Under that legal regime, the government can now acquire much more invasive information than it was able to decades ago. It's true that location records can vary in precision. But as Justice Sonia Sotomayor noted, that information may grow more and more accurate as technology continues to develop.

During arguments before the court, the justices seemed open to ruling that a government request for some large amount of phone location records could tip over into a Fourth Amendment-protected search of private information. Yet the question of just when a government request becomes too invasive is a complex one. Should law enforcement, as the ACLU argued, have to obtain a warrant for more than 24 hours’ worth of data? What information besides location records would newly be categorized as a search? “This is an open box,” Justice Stephen G. Breyer commented. “We know not where we go.”

Whatever the Supreme Court rules, it's past time for Congress to raise the standard for longer-term, larger-scale location record requests. For inspiration, lawmakers can look to state legislatures that have constrained authorities from warrantless requests for, variously, real-time location tracking, historical records, or both — though they must be careful not to overburden law enforcement in emergency situations. The high court may not know where to draw the line on privacy. But Congress, unlike the courts, is in the business of line-drawing.