Here's Apple's background on the invention: "A computer mouse is a small device that a computer user pushes across a desk surface in order to point to a place on a display screen and to select one or more actions to take from that position. The mouse first became a widely-used computer tool when Apple Computer Inc. of Cupertino Calif. made it a standard part of the Apple Macintosh line of computers. Until the late 1990s, most computer mice were opto-mechanical in nature that required a number of moving parts to work in tandem with some form of optical emitters/receiving device (such as an infrared LED/infrared sensor) to provide tracking information to a processor coupled thereto arranged to generate coordinate data that is used to move an on-screen icon (such as a pointer). Since this process is repeated hundreds of times a second, the motion perceived by a computer user is smooth and continuous.

"The use of mechanical components in the computer mouse limited the use of the computer mouse. However, towards the end of the 1990s, Agilent Technologies developed and introduced a purely optical mouse that in its first incarnation used a tiny camera that took over 1500 images every second to provide the requisite tracking information enabling the optical mouse to operate on almost any surface. Typically, the optical mouse includes a small, light emitting diode (LED) that bounces a beam of light off of a surface onto which the mouse was placed to be received by a light sensor (typically a CMOS type sensor). The CMOS sensor, in turn, transmitted each of the images to a digital signal processor (DSP) for subsequent analysis. Such analysis includes detecting patterns in the images and how these patterns moved since most recent previous image. The observed change in patterns over a sequence of images provides the requisite input data for the DSP to determine how far the mouse has moved which is then provided to a processor that calculates the corresponding coordinates for a computing device coupled thereto.

"Since it was now possible to use an optical mouse on most surfaces, a next step in the evolution of the computer mouse resulted in a wireless mouse connected to the computing device only by way of a wireless link. Such wireless links include those based upon the Bluetooth specification which is a computing and telecommunications industry specification that describes how mobile phones, computers, and personal digital assistants (PDAs) can easily interconnect with each other and with home and business phones and computers using a short-range wireless connection.

"Although a wireless optical computer mouse provides great flexibility to the computer user, one weak point of currently configured wireless computer mice is the relatively short battery life due primarily to the large power consumption of the optical tracking engine and wireless link. For example, a Bluetooth wireless mouse with the industry standard optical tracking sensor (i.e., the Agilent 2030 manufactured by Agilent Inc of Palo Alto, Calif.) draws approximately 35 mA from the on-board batteries (usually standard AA batteries) when in the active mode while the associated Bluetooth/microprocessor chip draws on the average of 7 mA for a total of approximately 40 mA in active mode. A power consumption of this magnitude translates into approximately a 2 month battery life creating an inconvenience for the user not to mention the cost of replacing the batteries at such frequent intervals. One solution to the problem involves substituting rechargeable batteries but this, of course, necessitates the use of a recharging station.

"Therefore, what is required is a low power tracking solution. One such low power tracking solution is a hybrid computer mouse having both a low power accelerometer used in combination with an optical tracking engine to provide velocity or relative positional data with low tracking errors over a wide range of use."

And here's Apple's summary of the invention: "The invention described herein pertains to a wireless low power tracking device and methods of use thereof. In one embodiment, a method for operating a pointing device in a low power manner is described. The method includes receiving first tracking information from a first tracking device and periodically determining accuracy of the first tracking information. A second tracking device is activated and used to acquire second tracking information when said determining indicates that the accuracy of the first tracking information is inadequate. The first tracking device is substantially lower power device than the second tracking device.

"In another embodiment, a hybrid tracking system suitably arranged to provide tracking information to a computer is described. The system includes an optical tracking engine arranged to provide the tracking information to the computer, a low power inertial tracking engine arranged to provide the tracking information to the computer, and an adaptive duty cycle signal generator coupled to the optical tracking engine and the inertial tracking engine. In the described embodiment, the adaptive duty cycle generator is arranged to compare tracking information provided by the accelerometer and provided by the optical tracking engine. When the comparison is valid, the adaptive duty cycle signal generator provides a first duty cycle signal that deactivates the optical tracking engine such that only the low power tracking engine provides the tracking information to the computer.

"In yet another embodiment, computer program product for operating a pointing device in a low power manner is described that includes computer code for receiving first tracking information from a first tracking device, computer code for periodically determining accuracy of the first tracking information, computer code for activating and using a second tracking device to acquire second tracking information when said determining indicates that the accuracy of the first tracking information is inadequate, wherein the first tracking device is substantially lower power device that the second tracking device. The computer code is then stored in a computer readable medium."

The inventors are Steve Hotelling, Joshua Strickon, Brian Huppi and Christoph Krah. FIG. 1 shows a block diagram of an exemplary wireless hybrid computer mouse in accordance with an embodiment of the invention.