Bluetooth Smart Scanner is the fastest app to find all Bluetooth Low Energy (also known as Bluetooth 4.0 or Bluetooth Smart) devices around you. It shows detailed information that Bluetooth Low Energy devices advertise, including device name, signal strength (RSSI), supported services, battery level, etc.
The app can be used for discovering and debugging Bluetooth Smart devices, by the professionals and people who are just curious.
Note that Bluetooth Smart Scanner only works on iPhone/iPad/iPod with Bluetooth 4.0. For now, these are iPhone 4S/5/5C/5S/6/6Plus, iPad 3/4/mini/Air and iPod Touch 5. BLE devices can only be discovered when they are advertising.