The results were published in the Journal of Alzheimer's Disease.
It can also pick up swine flu and bird flu.
The study asked over 75,000 people about the 23 symptoms most commonly associated with long COVID.
A study found air flow is slowest in the center of the train car, yet this has no affect on an individual's vulnerability.
Information is based on skin temperature, pulse, blood flow, sleep patterns, breathing and heart rate.
The condition affects between eight and 12 percent of jabbed people who catch the virus, the researchers say.
In the study, participants examined 72 students and 43 medical interns at a university and tracked data from Fitbits and self-reported COVID-19 diagnoses.
It detects temperature changes when the virus binds to nanoparticles molecularly impressed on a 3D printed device.
When people are out and about with pals they take fewer precautions against the deadly bug, say scientists.
It is believed more than half of people who catch coronavirus could end up with some form of long COVID-19.