Vibrating magnetic tattoos may one day be used to alert mobile phone users to phone calls and text messages if Nokia follows up a patent application.

The Finnish company has described the idea in a filing to the US Patent and Trademark Office.

It describes tattooing, stamping or spraying "ferromagnetic" material onto a user's skin and then pairing it with a mobile device.

It suggests different vibrations could be used to create a range of alerts.

The application lists Cambridge-based Zoran Radivojevic as the innovation's lead inventor. It was filed last week and was brought to light by the Unwired View news site.

It suggests a magnetic marking could be attached to either a user's arm, abdominal area, finger or fingernail.

"Examples of... applications may be low battery indication, received message, received call, calendar alert, change of profile, eg based on timing, change of time zone, or any other," the filing reads.

"The magnetic field may cause vibration of one short pulse, multiple short pulses, few long pulses... strong pulses, weak pulses and so on."

The filing also suggests that the magnetised marking could be used as an identity check. It says that by picking a certain shape the user could create a "specific magnetic impedance" - effectively their own magnetic fingerprint.

It says this could act as a "password" and gives the example of a laptop refusing to display content on its screen unless it verifies its user is close by.
'Invasive procedure'

Nokia is far from the only technology firm investigating new uses for haptic - or touch - feedback.

HTC and Samsung have released mobile phones that slightly vibrate when the user types or presses graphical-representations of buttons on their screens.

Engineers at the University of Utah are developing a video games controller that uses haptic feedback via the user's thumbs to create the sensations of waves, pulses and a bounce effect.

Researchers at the University of Leeds have also created a handheld prototype designed to let cancer specialists locate and categorise patients' tumours by how dense they feel while examining them from a remote location.

However, Nokia's idea stands out for seeking to enhance touch feedback by permanently, or at least semi-permanently, marking the users' body.

"Our research suggests that once a user become accustomed to haptic feedback on a phone or tablet screen, other devices that don't offer it can feel 'dead'," Marek Pawlowski, editorial director at the mobile industry research firm PMN told the BBC.

"Nokia's patent suggests that their magnetic mark could be invisible - which might make this appealing to some. But in the immediate term I think users would draw the line at anything that is invasive like a tattoo or would be seen to have potential medical effects."

A spokeswoman for Nokia was unable to confirm whether Nokia intended to follow up its patent application with further research.

neat idea!