It has become an iconic image of the coronavirus outbreak in China: a masked official aiming what appears to be a small white pistol at a traveler’s forehead.
For weeks, this ominous-looking device has been deployed at checkpoints across China — tollbooths, apartment complexes, hotels, grocery stores, train stations — as government officials and private citizens screen people for fevers in an effort to prevent the spread of the deadly coronavirus.
Sometimes described as a “thermometer gun,” the device is equipped with an infrared sensor that can quickly measure surface temperature without making any contact with a person’s skin. In recent years, it has become an important tool for countries scrambling to contain viral outbreaks. It was widely used to try to slow the spread of SARS in China in the early 2000s and to curb the Ebola outbreak in West Africa a decade later.
But for all of its powerful sensing technology, the thermometer has ultimately proved to be an ineffective defense mechanism, according to medical officials and experts on infrared devices. Like the surgical masks that have become ubiquitous in China, thermometer guns tend to be unreliable outside carefully controlled health care settings.
The thermometers determine temperature by measuring the heat emanating from the surface of a person’s body. Often, however, those wielding the tools don’t hold them close enough to the subject’s forehead, generating unusually low temperature readings, or hold them too close and get a high reading. The measurements can be imprecise in certain environments, like a dusty roadside, or when someone has taken medication to suppress a fever.