The magnets inside iPad Smart Covers could switch off pacemakers if the findings of a 14-year-old's scientific experiments turn out to be true. While putting together a science fair project Gianna Chien made the discovery and should be presenting her findings to 8,000 doctors at a Heart Rythm Society meeting in Denver, Colorado.

The danger comes from the small magnets inside the iPad Smart Cover, which are used to keep it attached to the front of the tablet's display. If you were to fall asleep with the tablet lying on your chest, those magnets could interfere with a pacemaker and switch it off.

"The research offers a valuable warning for people with implanted defibrillators, which deliver an electric shock to restart a stopped heart," said John Day, head of heart-rythm services at the Intermountain Medical Center.

Apple's product guide for the device does say a minimum of six inches should be kept between tablet and pacemaker.

As many as 30 per cent of people tested in Chien's study said they were affected by the device. Defibrillators will switch back on after the magnet is removed but some need to be reactivated manually.