Physical aspects as dexterity and motricity or cultural as gender and beliefs influence our smartphone using habits. These aspect can be anticipated from personnal but "privacy preserving" factors as sex/gender, age range, country.

Caution, the app must not discriminate a person (deduct she's more or less exposed to the virus) due to gender, age, etc. Preliminary tests must make sure it's not the case.

Social factors

Gender specifically influences our clothing We can't directly deduce cultural habits from gender (not either gender from biological sex) but we could consider different probabilty. Probability of wearing slim pants (with small front pockets), wearing a skirt (without pocket) - specially during summer, using a purse differ depending gender.

*source: boutiqueimpact.com

Age range/generations Some kids and teenagers have a smartphone but with specific usage rules due to family, school. The habits and the way we interact could change according to your generation. (features used as texting, vocal messages, video call)

(Due to advanced age, some people wont use their smarthone a lot (lack of dexterity and hearing). They are often the same who need close and physical help.)

"Turning off" your phone is an information to consider. Some "risky activities" as team-sports require to leave your phone (on or off) on the locker, car or home. One of the "hot spot" in the begining of COVID-19 epidemic in europe was a religious gatering in Mulhouse. We should consider in a specific context people could leave/turn off/put in airplan/silent mode for different reasons (respect the others, not be distract, personnal or familial rules). So "phone mode" could be consider (according to the battery level)

Using earphones/headphones change our gesture. Could "screen/earphones" sharing be detected? A very close and "long" (mor than 15min) human-to-human interaction is watching a video or listening to music with earphones together. It can't be detect as "very close interaction" by BT if one phone is in the pocket and used as "movie screen".

*source: fitnessvsweightloss.com

Device factors

Size

Your smartphone size specially influence the pocket you use. This factor could be linked to "clothing extrapolated"

Price and "style"

Does-it modify the way you leave it on a restaurant table by exemple? Or can it suggest your "social level" and habits?

Specific devices