How effective are thermal scanners in detecting people infected with the new coronavirus?
Thermal scanners are effective in detecting people who have developed a fever (i.e. have a higher than normal body temperature) because of infection with the new coronavirus.
However, they cannot detect people who are infected but are not yet sick with a fever. This is because it takes between 2 and 10 days before people who are infected become sick and develop a fever. See also: How to use hand sanitizer?