Ellume’s test starts with a self-collected nasal swab, which is plugged into a cartridge and analyzed, and its data is transmitted to a smartphone via Bluetooth.Credit...Ellume, via Associated Press

People as young as 2 are cleared to use the test, which takes just 15 to 20 minutes to deliver a result. Unlike many similar products, which are only supposed to be used by people with symptoms of Covid-19, this test is authorized for people with or without symptoms.

The test, developed by the Australian company Ellume, detects bits of coronavirus proteins called antigens. It’s slightly less accurate than gold standard laboratory tests designed to look for coronavirus genetic material using a technique called polymerase chain reaction, or P.C.R. But in a clinical study of nearly 200 people, Ellume’s product was able to detect 95 percent of the coronavirus infections found by P.C.R., regardless of whether the infected people felt sick. It also correctly identified 97 percent of the people who received negative laboratory test results.

Like other antigen tests that have received the F.D.A.’s emergency stamp of approval, Ellume’s test performs best within the first few days after a person starts experiencing Covid symptoms. In people without symptoms, the product found only 91 percent of the coronavirus infections discovered by P.C.R.

Dr. Valerie Fitzhugh, a pathologist at Rutgers University, noted that all of the study’s false positives occurred in the asymptomatic group. That “does make me a little nervous,” Dr. Fitzhugh said. False positives could send people into unnecessary periods of isolation or erode trust in testing.

Ellume, which was awarded a $30 million grant from the National Institutes of Health, plans to manufacture and deliver about 20 million home tests to the U.S. within the first half of 2021. The tests are expected to cost about $30 or less.

The test’s price tag — compared with some competitors that cost just $5 — and limited availability will likely restrict it from very frequent use.

But a test that can ping back immediate results could allow someone to promptly begin their isolation and break the chain of transmission. People carrying the virus are thought to be most contagious in the few days before and after their symptoms start, if they experience symptoms at all.

“I think this is hugely impactful, potentially,” Dr. Butler-Wu said.

Ellume’s test starts with a self-collected nasal swab. Plugged into a cartridge, the sample is analyzed, then the data is pinged to a smartphone via Bluetooth. The results go to the person taking the test, and can be shared with health care providers, as well as public health authorities.