How to detect a phone

[Robert]

Is it possible to detect a bluetooth (BLE) enabled phone when it enters the room?
I like to use the nrf51822 (BLE-Peripheral or BLE-Central) to detect any phone when it is in range.
Preferably without any app running on the phone, but I have no idea if it is even possible.

I found an almost similar question here, but the answer involved changes at the phone end.

Any help is greatly appreciated.
Regards, Robert

[Robert]

Thanks for your quick response.
When I do a scan with a tablet it will detect my phone as a device that is in range, without any app running on that phone. So my simple conclusion would be that it should also possible using the nrf51822. But I'm probably missing something.