When Austin-based Everlywell unveiled a new test for the coronavirus that people could buy online, use at home and mail back with results in 48 hours, the company was confident the product would be a hit.

The botched rollout of the federal government’s testing effort had left consumers hungry for alternatives. The company, which sells a variety of other home tests, was “inundated” with requests for a coronavirus one, said chief executive Julia Cheek on March 19, four days before it planned to put 30,000 tests up for sale at $135 each.

But then the Food and Drug Administration stepped in, warning consumers that no home tests had been approved and urging them to avoid the products. Everlywell’s debut was derailed. So were those of two other home-testing companies. Now people are wondering whether and when there will be a home test for covid-19. In a country where almost everyone is stuck at home, using on-demand delivery for everything from tonight’s dinner to today’s lesson plan, the notion of home testing has wide appeal.

Home tests would also allow people to test “without leaving home and risk infecting others, or themselves,” said Elliott Millenson, who developed the first home test for HIV.

But what seems like an obvious idea turns out to be complicated. And while the FDA has repeatedly signaled its interest in home testing — which appears to be a priority of the Trump administration — the agency also has made clear it wants more evidence that the tests work.

One issue is whether consumers can swab their noses correctly. Another is whether the samples can get to the labs quickly enough, and at the right temperature, to prevent changes in the virus that would produce inaccurate readings. Yet another involves instructions to consumers: What should companies tell them to do while waiting for results — and after they get them?

In recent days, the FDA took a major step that could help clear the way for home testing. It started allowing individuals to use short swabs to collect samples from the front of their nostrils — but only at drive-through testing sites, hospital parking lots and clinics where they are handed the swab by a health-care worker, then hand it back.

The approval of self-swabbing is critical to health-care workers staffing the sites who have been using long swabs to reach deep inside the individuals’ nasal passages and throat. Those providers have to wear personal protective equipment, which is in short supply.

Self-swabbing “could be a game changer at a time when we will need to find ways to relieve stress on our health care system, reduce risk to our health care workers, and scale up equitable access to testing in the United States and around the world,” Dan Wattendorf, director of innovative technology solutions at the Bill and Melinda Gates Foundation, wrote in a blog post. The foundation and UnitedHealth Group provided the FDA with data showing self-administered swab tests were as accurate as doctor-administered ones.

Most of the home tests being discussed, including Everlywell’s, are versions of the main diagnostic tests for the coronavirus being used across the country by hospitals and labs. These antigen tests are designed to tell whether a person is infected and use a technology called PCR to detect the virus.

A recent Journal of the American Medical Association Health Forum article detailed how the process could work as a home test: A person with symptoms would communicate by phone or video with a doctor about whether a test was appropriate. If so, the test would arrive through the mail or could be picked up at a pharmacy. The consumer would swab himself or herself and mail or deliver the kit to a laboratory for processing. Results would be available in days.

Kavita Patel, an internist and health-care policy expert at Brookings Institution who co-wrote the article, said such “self-service” kits would be the quickest way to ramp up testing, which besides helping patients would also provide public health experts with important information about the virus’s spread.

“Home testing is one of the few ways we can have some semblance of community surveillance,” she said.

But critics worry that home tests would encourage unnecessary testing and say evidence is still lacking that the tests are accurate.

XinQi Dong, director of the Institute for Health, Health Care Policy and Aging Research at Rutgers University, said unreliable tests could produce false negatives, indicating people were not infected when in fact they were.

“They might touch a family member when they shouldn’t,” Dong said. “It provides a false sense of reassurance that has unintended consequences.”

In addition, the tests would have to be processed by commercial laboratories that already are swamped by other tests and are experiencing supply shortages.

There are other types of home tests. California-based start-up Scanwell Health is developing a blood test that would detect two antibodies made by the immune system when a person is exposed to the covid-19 virus. The level of antibodies is a key indicator of infection. And if a person has antibodies but no symptoms, that person can have a level of reassurance about going back to work or helping others who have the virus.

The test would be available online, but only after approval by a nurse or physician. Customers would use materials in a kit, prick their fingers, apply a small drop of blood and two drops of a Scanwell solution onto a Scanwell card or strip that changes color. A smartphone app adjusts for color and shadows and sends a photo to doctors and nurses working for a nationwide company called Lemonaid. Scanwell would also work closely with Innovita, an established Beijing-based firm that makes 500,000 test kits a day, and has been approved by the FDA for use in professional settings.

Jack Jeng, a physician at University of California at San Francisco and chief medical officer at Scanwell, said the firm expects to get FDA approval in “days to weeks” and to have a product available in four to seven weeks at a total cost of $70.

Experts watching the FDA closely say it seems unlikely the agency would approve direct-to-consumer tests that don’t involve a doctor.

The companies that already tried to launch home tests said they were answering the call of the FDA. The government, facing a daunting shortage of testing kits after the failure of the initial Centers for Disease Control and Prevention test, in late February issued a policy to expedite the manufacture and distribution of tests across the United States.

Some tech entrepreneurs involved in developing the tests said they found the FDA overly bureaucratic and said the agency did not take advantage of the innovation that followed its Feb. 29 policy relaxing some requirements. They spoke on the condition of anonymity because they didn’t want to anger FDA officials.

But the agency has said repeatedly that those more flexible policies do not apply to at-home tests and that the companies that sell them must get approval, called an emergency use authorization.

Besides Everlywell, two California firms, Nurx and Carbon Health, had started to ship in-home sample collection kits at about $160 each.

Nurx launched its covid-19 self-collection testing and online consultation service on March 20. The lab they worked with, Molecular, complied with standards set by the Centers for Medicare & Medicaid Services and was licensed in Washington state.

The evening of the Nurx service launch, ​the FDA issued a news release​ saying that it was ”beginning to see unauthorized fraudulent test kits that are being marketed to test for covid-19 in the home.” It added that it saw the value of self-testing and was working with developers but stressed no product had gotten the required authorization.

Nurx immediately pulled its test and gave refunds to its customers. It says it believes its tests are accurate.

Carbon Health also withdrew its test. It had developed a test that uses a saliva sample from the cheeks and the roof of the mouth, instead of the nasal and throat swabs. The company said it was trying to avoid the supply chain issues that have plagued the nasal and throat swabs.

Both companies’ tests were retailing for over $160.

Everlywell, a five-year-old company that specializes in home testing kits for everything from allergies to fertility, said its test kit includes swabs for collecting samples, shipping materials to ensure safe transport and processing by labs that have FDA authorization. It initially said it would connect anyone testing positive to physicians and report the test results to federal and state agencies. But customers would not need advance approval of a physician.

It said its proposed $135 price was designed to cover its costs.

“I do believe the testing should be free,” said Cheek, the chief executive. “But with zero profit dollars to us. I know that may still seem high to people.”

Now the company is just shipping its tests to hospitals, clinics, nursing homes and assisted-living facilities. It plans to ship out thousands more by the end of the week. Everlywell said on its website that it would allocate the initial batch of tests to health-care companies “with workers on the front lines to get these tests in the hands of those who need them most urgently.”

Of the FDA’s guidance, Everlywell spokeswoman Christina Song said in an email: “This is novel territory for a lot of people — nobody has had to deal with a pandemic in America in our lifetimes — so it makes sense that everyone is operating with the information as they have it."

Song said the company is still discussing with the FDA “a path forward for an at-home sample collection test.”

Nitasha Tiku contributed to this report.