A good pulse oximeter has a Perfusion Index (PI) and an OLED display with large numbers. The PI indicates if you’re getting a bad reading but the pulse is weak. The OLED display is bright and easy to see.
Yes, you can and you should use a pulse oximeter to check for COVID-19 symptoms, according to Doctors Christy Reisinger and Richard Levitan. Both doctors treat COVID-19 patients. They both report that low blood oxygen is a seen in most if not all patients infected with COVID-19.
I can smell dog fur when I vacuum the carpet. This means my vacuum cleaner is sucking in dog fur, and then shooting some of it back into the air! I am a senior citizen. Vacuuming is too much work to put up with this mess. Should I get a certified vacuum cleaner and a certified air cleaner?
For airborne allergens, the best allergy device is a HEPA air purifier. The best air purifier will be the one that not only cleans the air, but also has the sense not to wake us up at night with lights and noise.