By Mark Ward BBC News Online technology correspondent

Tiny sensors used to improve car safety could soon be helping people get more out of handheld computers.

Researchers at Microsoft's Cambridge campus in the UK are putting sensing devices used to trigger airbags into handhelds to help create virtual 3D images on the computers' screens.

When a handheld fitted with the sensor is angled, its screen shows different parts of an image giving a pseudo-3D effect.

It also allows the palmtop computer to display pictures and documents far larger than would otherwise fit on the small screen.

Angle finder

Handheld computers are convenient for many reasons. But their small screen, often only 240 by 320 pixels in size, can detract from their usefulness if they are used to look at a large document such as a spreadsheet or a web page.

Tilt sensors are used to trigger airbags

Now, Microsoft researcher Lyndsay Williams might have found a way to help handhelds and PDAs display larger images and documents, but without increasing the size of the screens.

Ms Williams has fitted tilt sensors on a handheld computer so it can work out at which angle to the horizontal it is being held.

The micro-machined tilt sensors, which cost about �1.50, are typically used to trigger airbags in cars by measuring sudden changes in acceleration or deceleration.

On a PDA, the sensor triggers the device to show a different part of an image depending on how it is being held.

The sensor makes the screen act like a square hole in a piece of paper being slid over a larger document or image underneath.

Distorted perspective

Ms Williams said that moving the device around would give users a view of an image or document far larger than one that could fit on the screen.

Some work had to be done to prepare pictures of real world objects to be displayed this way, she said.

Pictures are given the pseudo-3D look by having their perspective distorted so that the elements at the rear of the image look smaller.

Antonio Criminisi from Microsoft's lab in Redmond, Washington, US, prepared a 3D version of Masaccio's La Trinita - the original is in the church of Santa Maria Novella in Florence, Italy - to test out the 3D system.

Building up the 3D images from distorted layers makes them larger than the more regular "flat" images. But Ms Williams said the advantage was that it might make PDAs less of a chore to use.