How to know if a device comes into my WiFi network range even though it does not connect to my network [closed]

How to know if a device comes into my WiFi network range even though it does not connect to my network [closed]

How to know if a device comes into my WiFi network range even though it does not connect to my network?

Here my business model is that when someone comes into my Wi-Fi range if I can know the count of it for suppose I run a restaurant every time I cannot be there but when I can know the count of the people, then I can say these many people come to my restaurant in this particular time and I can provide analytics for every 1hr or 10 min. Then I can know the people I need to keep for work at my restaurant at that particular time. This is simply my intention. Here generally WiFi is turned on the everyone's mobile.