Using ESP8266 to trace mobile phones.

I am working on a project where I need to scan mobile phones using WiFi modules. The only thing is that the phone's wifi need not always be connected to any AP. As in even if the phone's wifi is just turned on, without connecting to any access point, my device should detect the phone. Now my queries:

  1. Is this project possible ?
  2. If yes, can ESP8266 the normal Wifi module or NodeMcu serve the purpose?

Thank you

Is that legal?

Please don't do it to my phone.