Fever does appear to be one of the first symptoms of Covid. One thing that is recent in the news is that 98.6 my not be the “normal” temperature. Now they are saying 97.?. Mine has always been in the high 97 area. Second way to test would be a smell detector. You could have say, 3 pieces of blotter with a very weak scent, a moderate scent, and a strong scent. Possibly 2 sets, one with 3 noxious scents and one with 3 pleasant scents. Have each person who has a low temperature then smell a weak sc with 3 noxious scents and one with 3 pleasant scents. Have each person who has a low temperature then smell a weak sent. If they can’t smell that smell the other weak scent. If both are not smelled, then try the 2 medium scents. Then the 2 strong scents.
Since sense of smell and taste are often the first to go, even before symptoms, they could then be told to take, or give zinc or calcium/magnesium/zinc supplements to start taking immediately. And more closely monitored even if the temperature seems normal. Perhaps asked to wear a face mask or put to work where they can maintain social distance.
Scratch and sniff COVID test. I like it!
My normal temp seems to be 97.3. I never have had much of a sense of smell and my wife tells me I have no taste.