An Apple patent (number 20120226774) for "display snooping" has appeared at the U.S. Patent & Trademark Office. It's designed to provide displays that may be used as secondary display devices.
Per the patent, circuitry may be placed in a communication pathway between a host computer and a second display device external to the host computer. One example provides an interface circuit that receives communication signals from a host computer. These signals may be AUX signals sent over a DisplayPort or Thunderbolt connection. The interface circuit may pass these signals to the second display device directly, it may modify them before passing them on, it may ignore them, or the interface circuit may pass them to a processor associated with the second display device.
Here's Apple's background on the invention: "Computing environments continue to evolve. One of the latest evolutionary steps is the use of more than one display screen to view data generated by a computer system. For example, a computer designer may use one display to show a schematic of a portion of an electronic device and another display to show a layout of that portion of the electronic device.
"The inclusion of multiple displays is driven by many factors. For example, computing tasks are becoming more complicated. These tasks are being handled by more powerful programs and computing resources, which are able to provide multiple graphics images. Also, the costs of such displays and associated hardware have been reducing as the quality has been increasing. Moreover, users are becoming more skilled and are able to handle more data.
 These displays may be of various types. For example, they may be dedicated displays that are separate from computing devices. They may also be displays that are integrated into a computing device, such as a desktop, all-in-one computer, laptop, netbook, tablet, ultrabook, or other such device.
"It is often fairly straight-forward to use a dedicated display as a second display. Dedicated displays are configured to accept not only video information from an external source, but control signals as well. These control signals may include signals to adjust brightness, audio levels, resolution, and others.
"Display panels that are integrated with, or are connected to, other devices may not be so flexible, however. These displays may be configured to communicate these signals with the computing devices of which they are a part. They may not be configured to accept signals from external computing devices. As such, these displays may not be as suitable for use as a second display device.
"Accordingly, what is needed are circuits, methods, and apparatus that provide displays that may be used as secondary display devices."
Ronald R. Hochsprung is the inventor.