Read the full article on The Conversation. From the article:

Even if infrared thermometers could detect fever reliably, they could not detect COVID-19 reliably. Nor could any other thermometer. Patients with COVID-19 are not guaranteed to have a fever. Recent research indicates that many people who test positive for COVID-19, and especially children, never have any detectable sign of illness, including fever.

Reference information: Fuller, A. Mitchell, D. 2020. "So you think investing in fever screening can curb the spread of COVID-19? Think again". The Conversation.