Verily Life Sciences, a sister company of Google, scrambled to introduce a free coronavirus-screening site for the public and set up testing locations in March after President Trump made an off-the-cuff announcement about the program. It had a rocky start, but has since helped more than 220,000 people get tested in 13 states.

Now, the company has its sights set on employers. It is introducing a health screening and analytics service for businesses trying to safely reopen during the pandemic.

The service, announced on Thursday, will offer Covid-19 diagnostic testing for employees and clear them to return to the workplace based on their test results and other health data. It will also make recommendations to employers on how often workers should be retested, based on the prevalence of the virus in their work force and the local community.

“Employers are really focusing on how to ensure that they are not the source of another outbreak,” said Dr. Vivian Lee, the president of health platforms at Verily, a unit of Google’s parent company, Alphabet. “And that they do not wind up in a situation where they’re putting the safety of their employees at risk when they need to be back in an office or a workplace setting.”

With its new service, Verily is joining numerous tech giants and start-ups rushing to help business across the United States as they grapple with how to safely reopen the workplace. Microsoft and the large insurer UnitedHealth Group, for instance, recently collaborated on a free symptom-checking app that helps pinpoint workers at obvious risk for the virus and direct them to testing resources. On Tuesday, Fitbit introduced a program that includes a daily symptom-checking app for employees and a work force health-monitoring dashboard for employers.

Kogniz, an artificial intelligence start-up, is marketing thermal camera systems as coronavirus fever-screening and “social-distancing enforcement” tools for the workplace. And Jvion, another A.I. start-up, is marketing an “employer recovery package” to predict the risk of employee exposure to the virus and likelihood of developing it.

There is such a glut of new coronavirus risk-reduction products that it’s a challenge for many employers to assess them all.

“A big market rose up overnight,” said Jeff Becker, a senior analyst for digital business strategy at Forrester, a market research firm, who recently surveyed two dozen vendors offering coronavirus solutions for employers. “But it’s a fractured ecosystem, much like traditional health care.”

To address the fragmented market, Verily and other health companies are introducing more comprehensive health-screening programs for employers, complete with Covid-19 lab tests and health counseling for employees who test positive. The new services are also trying to mitigate a pressing problem for employers: Perhaps one quarter or more of people who have the virus do not experience symptoms like fevers and coughs. That means symptom-checking apps and fever-scanning cameras could clear employees who have the virus to return to the workplace, where they might inadvertently infect their colleagues.

Color, a Bay Area health technology company whose labs are processing Covid-19 tests for the City of San Francisco, reported on Monday that, among a group of 30,000 people it tested for the virus, the majority of those who tested positive had mild or no symptoms.

“Things like fever checks, fever screening — those things are actually not going to prevent transmission in a workplace setting,” said Caroline Savello, the chief commercial officer at Color, which recently introduced a testing program for employers.

Many medical centers, nursing homes and other high-risk facilities for essential workers have already adopted such employee-testing programs. Color’s program for businesses that are reopening involves testing employees for the virus at least once before they return to the workplace, and then testing asymptomatic employees again at regular intervals.

“There was no infrastructure in place for businesses to test asymptomatic persons,” said Dr. Sekar Kathiresan, the chief executive of Verve Therapeutics, a biotech company in Cambridge, Mass., that began using Color’s program in May in a pilot test with 11 other local biotech firms.

The biotech employees visit a central site once a week to have a nurse practitioner swab their noses, he said, at a cost of $ 130 per test. In 704 tests over the first month, he added, none of the employees had positive results.

“This gives our companies, our employees great peace of mind because they know that everybody that’s coming into the laboratory to do the research is negative,” Dr. Kathiresan said. “So it’s an expense that is well worth it.”

He said he expected employee-testing costs to decrease significantly over time as home self-collection kits, which allow people to swab their own noses or collect saliva samples and then send them to labs, became more available.

Federal health authorities, however, have so far provided little guidance for businesses on testing employees for coronavirus.

In late May, the Centers for Disease Control and Prevention published guidelines on “Resuming Business,” which recommended that employers prepare a “plan for conducting daily in-person or virtual health checks (e.g., symptom and/or temperature screening) before employees enter the facility.” But the guidelines mentioned employee testing for the virus only in passing.

One concern is that the diagnostic tests could give employees a false sense of security, public health experts said. Because the virus can take several days to develop, they said, the time between taking a test and getting the lab results back could cause some employees who have the virus to receive false negative test results. Despite comprehensive testing, for instance, a group of Army recruits and instructors at Fort Benning, Ga., recently suffered a major outbreak of the virus.

Another concern is that scaling employee-testing programs nationwide could lead to unnecessary medical screening — particularly for workplaces where employees, wearing masks, can be spaced far enough apart to adhere to social-distancing guidelines — and might overwhelm labs that are running more urgent coronavirus tests for patients with serious symptoms. And some employees may object to being required to take medical tests and have the results automatically sent to their employers.

Dr. Lee, the Verily executive, said the company would consult with employers to tailor virus testing and workplace safety protocols to the number of their employees, workplace locations, the prevalence of coronavirus in the local community and the type of work employees performed.

“Truck drivers are different than meatpackers in terms of susceptibility,” Dr. Lee said. She added that the first client for Verily’s employer program, Brown University, planned to begin pilot-testing it on Monday.

For many vendors seeking to sell employers on new workplace health and safety tools however, coronavirus solutions — which will quickly obsolesce once a vaccine is developed — are not the endgame, analysts said. They merely provide another opening for businesses to introduce new clients to their technology.

“The opportunity here is to start a relationship with these companies and not necessarily to generate revenue off of these sales right now,” Mr. Becker, the Forrester analyst, said.