Person (phone) detector that trigger an event esp32 cam
Detecting a phone could be easily done by capturing WiFi probe requests which are sent by phones having at least one saved WiFi network. Note that such requests alone are often enough to identify the person, if their home WiFi SSID is set to something like "Davids_wifi".

Software-wise, this would be much easier to do on Linux (think Raspberry Pi or a similar device) which already have all the network sniffing software like tcpdump, which you would otherwise have to find or implement on ESP32.

I'm leaving out the legal implications of what you're trying to do as I don't know what country you are in, but bear in mind that hidden surveillance may be illegal in some cases.