You have to start a scan for Classic Bluetooth devices with startDiscovery() and a scan for Bluetooth LE devices with startLeScan(). Caution: Performing device discovery is a heavy procedure for the Bluetooth adapter and will consume a lot of its resources.
Edit: On LG Nexus 4 with Android 4.4.2 startDiscovery() finds Bluetooth LE devices. On Samsung Galaxy S3 with Android 4.3 startDiscovery() doesn't find Bluetooth LE devices.
http://stackoverflow.com/questions/21809946/bluetoothadapter-startscan-vs-bluetoothadapter-startlescan/22524528#22524528