Amazon.com: Logitech Unifying Receiver, 2.4 GHz Wireless Technology, USB Plug Compatible with all Logitech Unifying Devices like Wireless Mouse and Keyboard, PC / Mac / Laptop - Black : Electronics
Amazon.com: Logitech USB Unifying Receiver - 2 Pack For Personal Computer : Electronics
Logitech Unifying receiver - Wikipedia
FreeKB - Logitech Resolve "There is no Unifying receiver plugged into your computer"