Why don't people just buy a temperature scanner for family gatherings?

Question

Covid-19

Answer 1

Why? That's because them scanners are made in China!

Answer 2

Because that doesn’t catch people who are asymptomatic but still contagious. 

Answer 3

Most people do own a temperature scanner.  They just do not think they need to use them.

Also the scanners are not reliable as a way of preventing the spread of COVID.  Some people never develop a fever but are still infected and can spread it.  You can also spread for a short time before the fever and after it breaks.  

While it would probably reduce the spread, it would not prevent all spreading.