Multiple report has confirm that people without symptoms are spreading the virus. Nigeria has a temperature reading device at the airport, but the italian was able to enter the country without been detected at the airport.

Infected people without symptoms might be driving the spread of coronavirus more than we realized
Elizabeth Cohen-Profile-Image
By Elizabeth Cohen, Senior Medical Correspondent
https://edition.cnn.com/2020/03/14/health/coronavirus-asymptomatic-spread/index.html

Right from day one , i have always believe focus should be on checking the breath pressure of every one, a person with any respiratory related illness breath pressure will be lower than people without respiratory illness. Those with lower breath pressure can then be set aside for further testing. This process will save time, money and help to stay ahead of the virus.

Breath Analyser in the market is use to detect alcohol consumption, but it can be re-configure to detect low breath pressure.

A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. A spirometer measures ventilation, the movement of air into and out of the lungs. The spirogram will identify two different types of abnormal ventilation patterns, obstructive and restrictive. There are various types of spirometers which use a number of different methods for measurement (pressure transducers, ultrasonic, water gauge)

Pulmonary function tests
Main article: Pulmonary function testing
A spirometer is the main piece of equipment used for basic Pulmonary Function Tests (PFTs). Lung diseases such as asthma, bronchitis, and emphysema can be ruled out from the tests. In addition, a spirometer is often used for finding the cause of shortness of breath, assessing the effect of contaminants on lung function, the effect of medication, and evaluating progress for disease treatment.[1]

Reasons for testing
Diagnose certain types of lung disease (such as asthma, bronchitis, and emphysema)
Find the cause of shortness of breath
Measure whether exposure to chemicals at work affects lung function
Check lung function before someone has surgery
Assess the effect of medication
Measure progress in disease treatment

https://en.wikipedia.org/wiki/Spirometer

You have a point.