Control output wihout connection

Question

Hi, 
 Is it possible to control the ouputs without connecting? 
 I mean something like this: 
 I have a nRF51DK. And I would like to detect if there are bluetooth devices in the area. If yes it should turn on a LED. 
 I dont want to use an application. It should automaticly detect the device, when it turns on the bluetooth. 
 And I would like to know if there is something like a unique bluetooth adress? Or is it possible to check the BD_ADDR adress? 
 So only predifened bluetooth adresses would turn the LED on

RK · Accepted Answer

I covered that in my original answer. You can only detect a device which is transmitting for a start - just having bluetooth 'turned on' means nothing. It could be on and idle, or scanning, if it's not transmitting, there's nothing to detect. 
 If a device is advertising you can detect it. Doesn't matter WHAT it's advertising (leaving the discussion about directed advertising aside) if it's advertising you can scan for it. But that's a pretty limited case. The last possibility is that it's in connection with another device - theoretically if you wrote lots of code you could find such devices eventually but there's nothing in the BTLE stack to help you. 
 So basically you can't just detect a device because it happens to have BTLE turned on, you can detect devices with BTLE on advertising something, and the something doesn't matter. Else, you can't.