Samsung SMO-3500B Optical Sensor Type Wireless 2.4Ghz 3 Buttons Ultra-Compact Receiver Optical sensor type / micro Nano USB receiver(18x15mm) Receiver built-in storage space. Wireless- 2.4Ghz (8M) Auto Sleep Mode (It convert if not using mouse to auto sleep mode.) Plug & Play (If will connect USB receiver to your computer will automatically set to the ID.) AAA bettery * 2 / Power on/off