Number of people inside a store = ?

[Lucky-Luka]

Hi all
Do you have an idea how I can check the number of people that go inside and go outside a single door store? I need to know how many people are inside. I would like to use Arduino. It's a project related to covid19 safety measures: not more than x number of people inside a y m^2 space.
Thanks

[Rerouter]

The usual approach is line break sensors, atleast 2 with an offset to tell direction, however unless you have a store with a forced entry and exit path and place the sensors where people do not stall, you will have to have a means of compensating for missed and extra counts.

Depending on the store may be easier to supply a staff member at the counter with an up/down click counter.

[Kleinstein]

The sensor may not work absolute reliable, e.g. counting legs / arms instead of people. So one would need means to correct (e.g. manually), possibly more than the natural one from negative numbers.