Logitech Unifying receiver
The Logitech Unifying receiver is an extremely small dedicated USB wireless receiver that allows up to six compatible Logitech human interface devices (such as mice, trackballs, trackpads, and keyboards; headphones are not compatible) to be linked to the same computer using 2.4 GHz band radio communication in a way very similar to, but incompatible with, Bluetooth. Because devices need to be paired with a receiver, it is impractical to use different receivers in several computers (e.g., with a desktop and a laptop computer) at the same time to allow a single input device to be used on all of them. Still, the receiver and input devices can be moved together from one computer to another.
The receiver that comes with a Logitech input device is paired with the device at the factory. When purchasing a stand-alone receiver (e.g., a replacement), pairing it with an existing device through the freely available pairing software is required.
Some (older) Unifying devices limit the number of allowable pairing changes to a maximum of 45 times. Once the 45th connection is made, it is no longer possible to connect such a device to a further, different receiver. For users who often switch a Unifying device between multiple PCs or laptops with individual receivers, this connection limit can become an issue. For example, a user who frequently switches a mouse between two receivers (e.g. at work and home) will quickly exhaust the limit of available pairing switches. Newer devices can switch pairings an unlimited number of times.
Pairing software is available for Microsoft Windows and Mac OS X from Logitech. Wireless devices using the Unifying Receiver are supported since Linux 3.2.  Software to manage Unifying devices on Linux is available from third party developers, like Solaar.
In addition, many companies have made USB wireless receivers very similar to Logitech's, though it is unknown if Logitech has taken legal action against these companies or even if Logitech holds a patent for the technology. Logitech devices are incompatible with many of these "off brand" receivers, though some are expressly designed as inexpensive alternatives to the Logitech Unifying receiver that can be paired with Logitech devices.
Logitech Unifying receivers (LURs) are often included in wireless Logitech keyboard, mouse, and combo sets, though they may be purchased alone. As of October 2017, the cost to purchase a LUR directly from Logitech is €12.99, or US$15.36. 
- Gallegos, Gary. "Gadgets: The Logitech Unifying Receiver (aka "fake bluetooth")". Archived from the original on 4 March 2016. Retrieved 23 February 2013.
- "Limitations on Unifying devices - Logitech Support Article". Retrieved 17 March 2015.
- "Linux Git commit: HID: Add full support for Logitech Unifying receivers". Retrieved 2 May 2013.
- "Logitech Parts Store for Wireless Comboolaar MK520". Logitech. Retrieved 4 April 2013.