Asus Bluetooth 4.0 usb adapter. The Asus USB-BT400 gives your system the ability to transfer data wirelessly to mobile devices and will allow use of Bluetooth keyboards and mice. Insert this USB BT400 Bluetooth adapter into a dedicated USB 2.0 port for best results. Bluetooth Dongle 4.0. The USB-BT400 is a Bluetooth Smart Ready USB adapter with Bluetooth 4.0 capabilities. It connects you with a multitude of compatible devices and supports Bluetooth Low Energy (BLE) to reduce power consumption. In dual-mode, the USB-BT400 maintains fully backward compatibility with Bluetooth 3.0, 2.1, and 2.