The latest Apple Powerbook laptops can now be controlled with a gentle shake, thanks to a clever software trick.

The new model of the notebook includes a motion sensor that locks the head of the hard drive in one position if the machine is suddenly dropped, to prevent damage as well as loss of data. The sensor is able to tell when the computer is moved up and down or rolled forwards or to the side.

But now software engineer Amit Singh, who lives in California, US, has found a way to turn the sensor into a novel means of controlling the system. As the sensor can be accessed using through the computer's operating system, Singh came up with some simple code to let him control things on the screen using movement.

Using the technique it is possible to manoeuvre open windows by shaking or shimmying the machine. Using another program Singh created, called the Orientation Visualizer, it is even possible to display a 3D image that appears to hang in space as the PowerBook is moved around it.

Research project

Singh says he began experimenting with the Apple Motion Sensor as research for a forthcoming book on Apple's Mac OS X operating system. But he says many other programmers have shown an interest in the trick.

"[It has] generated a substantial amount of interest, perhaps more than I had expected," Singh writes on a webpage documenting his exploits. "It is quite interesting to observe how one's fantasy is tickled by abnormal ways of doing the normal."

Rael Dornfest, chief technology officer at computer publishers O'Reilly, says the trick "digs into the nitty-gritty details of the underlying technology and provides some fascinating applications".