But Cuomo noted that New York would need thousands of investigators to make the system effective. And the information gleaned from personal interviews is based on sometimes faulty memories.

Contact tracing via cellphone doesn’t have those shortcomings, but it does raise privacy concerns.

The ACLU, in a recent white paper, cautioned that any system using cellphone data must be voluntary, encrypted, time-limited with a specific end point to the data collection, and conscious of the “rights of privacy and free association.”

The ACLU said technology-assisted contact tracing or TACT “is useful only if those who learn of possible exposures to COVID are able to do something about it: get tested, get counseling, get treatment, or take measures like self-isolation. The lack of adequate and equitable social and public health support systems would limit the effectiveness of any TACT system — potentially risking people’s privacy without bringing them benefits.”

Raimondo has said Rhode Island’s cellphone tracking would be opt-in, meaning cellphone owners would have to agree to be tracked.

“The State is developing an app that would allow for real-time monitoring of symptoms and would assist our contact tracing efforts in order to contain the spread and help prevent future outbreaks,” Raimondo press secretary Josh Block said in an email. “This app will operate on an opt-in basis, meaning no data will be collected without the user’s consent.”

Cybercriminals Seek Profit in Coronavirus Quick View Cybercriminals Seek Profit in Coronavirus State and local governments are watching for malicious emails preying on coronavirus fears.

But that’s not reassuring enough for some.

“Every American should have been concerned about privacy even before coronavirus,” said Rhode Island House Minority Leader Blake Filippi, a Republican who spearheaded the letter to Raimondo. “Voluntary systems sometimes get turned into involuntary systems. If it’s true it’s going to be voluntary, it’s a waste of resources. No one is going to be voluntarily tracked.”

In Colorado, Gov. Jared Polis, a Democrat, issued a stay-at-home order on March 25 and set up a voluntary system to track people with symptoms of the COVID-19 virus. People who are feeling sick can fill out an online form and provide cellphone information that allows the state to record their GPS data. Health officials can follow up with them.

Earlier, the state had used metadata gathered anonymously from phones to pinpoint areas where people were heeding stay-at-home orders.

And North Dakota rolled out a new app, Care19, that allows phone users to record their own movements. Other states are expected to follow.

Kansas is among several states using cellphone data to see where people are obeying stay-at-home orders — and where they are not. The Kansas Department of Health and Environment is using a dashboard from Unacast, a location data and analytics firm, that compiles phone GPS data.

That data is anonymous but can give officials an idea of areas where large numbers of people may not be heeding stay-at-home laws. The data led state officials to ramp up their pleas for people to stay at home.

As Protests Spread, States Tread Carefully to Avoid Inflaming Extremists Quick View As Protests Spread, States Tread Carefully to Avoid Inflaming Extremists “It is a tightrope that has to be walked.”

Kansas Senate President Susan Wagle, a Republican, questioned the use of the data and asked state officials to provide all records of the state’s “use of a third-party data collection program (such as Unacast) to track the movement of individuals through their cell phone data.”

Apple and Google announced they are developing an app that would use Bluetooth to trace smartphone users’ proximity to other users. The app will be designed to work with apps run by public health authorities. The functions will require users to opt in, the companies said. White House officials are in talks with the companies about how the data would be used.

Even health experts acknowledge that cellphone tracing, while effective, raises privacy concerns.

On Snapchat’s “Good Luck America,” Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases and a member of the White House coronavirus task force, said privacy under such circumstances creates “sticky issues.”

“You know, you could look at somebody’s cellphone, and say, ‘You were next to these 25 people over the last 24 hours,’” Fauci said. “Boy, I gotta tell you, the civil liberties-type pushback on that would be considerable. Even though from a purely public health standpoint, that makes sense.”

Border Checkpoints Discourage Travelers Between States Quick View Border Checkpoints Discourage Travelers Between States “That is not essential — to come into Delaware to buy alcohol.”

A Pew Research Center survey this month found more than half of adults said it was at least “somewhat acceptable” for the government to track the cellphones of people who tested positive for the coronavirus. Some 45% said it was acceptable for the government to track people who may have had contact with someone who tested positive.

But the survey found less support for monitoring smartphones to make sure people are following social distancing guidelines, at 37%.

And 60% of the more than 4,900 U.S. adults Pew surveyed said tracking people by cellphone wouldn’t help stop the spread of the virus, while just 38% thought it would. (The Pew Charitable Trusts funds both the Center and Stateline.)

Americans should be aware that the vast majority of the cellphones they carry already have GPS applications that keep track of where the phone owners have been, said Greg Kelley, chief technology officer of Vestige, a digital forensic and cybersecurity company headquartered in Cleveland.

That capability can be disabled, he said, but most users don’t do that. “Even when you disable it, I’ve seen instances where it’s still stored on the phone,” he said in a phone interview. “I was able to tell when this individual got up in the morning, went to school … where he went in the school, when he came back home, went to a restaurant, and home again.”

It wouldn’t take much for software companies to make that data available to outside entities, he said. “That’s where you get into civil liberties,” he said, adding that opt-in apps would address some of the concerns.

He noted that China has started requiring an app on phones that lights up with a specific color when the owner has been cleared to engage in certain activities, such as riding the subway. That might be problematic in this country, however.

Juliette Kayyem, senior lecturer in international security at Harvard’s Kennedy School of Government, said for the next two years or so, the nation may have to place a greater emphasis “on societal needs than individual privacy rights.”

“Much like rules require vaccination to enjoy certain privileges (like public school) we will get a version of that,” she said in an email. “If you want your total privacy, then you will lose privileges.”