Colleges that require virus-screening tech struggle to say whether it works.

Before the University of Idaho welcomed students back to campus last fall, it spent $90,000 installing temperature-scanning stations, which look like airport metal detectors, in front of its dining and athletic facilities in Moscow, Idaho. When the system detects a student walking through with an unusually high temperature, the student is asked to leave and get tested for the coronavirus.

But so far, the fever scanners, which register skin temperature, have flagged fewer than 10 people out of the 9,000 students living on or near campus. Even then, university administrators could not say whether the technology had been effective because they have not tracked students detected with fevers to see if they went on to get tested.

The University of Idaho is one of hundreds of colleges and universities that adopted fever scanners, symptom checkers, wearable heart-rate monitors and other screening technologies this school year. Such tools often cost less than a more validated health intervention: frequent virus testing of all students. They also help colleges showcase their pandemic safety efforts.

But the struggle at many colleges to keep the virus at bay has raised questions about the usefulness of the technologies. According to a New York Times database, there have been more than 530,000 virus cases on campuses since the start of the pandemic.

One problem is that temperature scanners and symptom-checking apps cannot catch the estimated 40 percent of people with the coronavirus who do not have symptoms but are still infectious. Temperature scanners can also be wildly inaccurate. The Centers for Disease Control and Prevention has cautioned that such symptom-based screening has only “limited effectiveness.”

The schools have a hard time saying whether — or how well — the devices have worked. Many universities and colleges are not rigorously studying effectiveness.

More than 100 schools are using a free symptom-checking app, CampusClear, that can permit students to enter campus buildings. Others are asking students to wear symptom-monitoring devices that can continuously track vital signs like skin temperature.

Administrators at Idaho and other universities said their schools were using the technology, along with policies like social distancing, as part of larger campus efforts to hinder the virus. Some said it was important for their schools to deploy the screening tools even if they were only moderately useful.

At the very least, they said, using services like daily symptom-checking apps may reassure students and remind them to be vigilant about other measures, like mask wearing.