If you’ve been watching the news, you’ve probably seen health officials using an infrared thermometer to check individuals’ temperatures before they’re allowed to go into grocery stores or other public buildings. It seems like an easy enough way to see if someone has a fever. However, there is some concern about whether or not they actually work.

The best feature of the infrared thermometers is that it allows for a quick read of surface temperature without having to actually touch that surface. In the case of COVID-19, the goal is to not actually touch the individual being tested. This is an incredibly important feature when trying to minimize the spread of a disease. For this reason, these devices were widely used in the 2003 SARS outbreak in China and the 2010s Ebola outbreak in West Africa.

The problem with these types of thermometers is that if they’re not held close enough to a person’s forehead, they’ll generate an unusually low temperature reading. If they’re held too close, you can get a false high reading. In addition, the measurements can be imprecise in certain environments, like being outside on warm day or if a person just finished exercising. Most companies who produce the thermometers state that they’re designed for quick screenings in an indoor environment and they’re not as accurate as traditional thermometers. If someone takes medication to suppress a fever, the thermometers aren’t going to be able to detect that. This is exactly what some individuals have done to make it past screening checkpoints.

Despite the evidence pointing to the inaccuracy of the infrared thermometers, the demand for them has increased sharply. As a result of the increased demand, there are shortages of them worldwide. In addition, prices have skyrocketed to three to five times the usual cost per industry experts.