We are used to smartphones communicating using their regular 3G, 4G, Wi-Fi and Bluetooth – but it turns out there's another way.
A system called Pulse uses the magnetic field sensor, or magnetometer, for the compass app in iPhones and Android phones, to receive messages in the form of a varying magnetic field produced by a nearby electromagnet.
The transmission rate is pretty slow – only 40 bits per second – and it only works over a range of 2 centimetres. But that has its own advantages, say Vassilis Kostakos and colleagues at the University of Oulu in Finland, who have built a test electromagnet system that communicated with Android phones to show that the idea works.
By encoding data in a varying magnetic field they have shown they can transmit anything from a web address to a MIDI music sequence from the electromagnet to the phone. That means a small electromagnet embedded in an interactive street poster could do the job of a printed QR code, say, but with the benefit of an advertiser being able to regularly change the URL.
"This is a live dynamic channel where information can be broadcast in real time. QR codes only have static pre-determined information," says Vassilis.
The idea could improve security for small payments too. The near field communications (NFC) radio signal that allows you to pay for goods with your phone can be read up to 20 centimetres away, meaning an eavesdropping attacker could steal cash from a phone if near enough – in a cafe queue, say.
Vassilis suggests that the magnetic messaging system could ensure the phone exchanges nothing until it is within 2 centimetres of the payment terminal – when the magnet would send a secure code that activates the regular NFC app.
But these applications are just early suggestions. In September, the Oulu team will reveal more of their plans for magnetic messaging at the annual ubiquitous computing conference in Seattle, Washington.
New way in
Perhaps other smartphone sensors could be adapted to send information in this way too, says Vassilis.
"With other sensors the efficiency of a communication depends on how quickly you can physically manipulate the sensed parameters," says Vassilis. "I'm not sure how well a barometer would work for instance – we need to quickly change air pressure to convey information which could be tricky," he says.
Andrew Campbell, head of the Smartphone Sensing Group at Dartmouth College in Hanover, New Hampshire, says the Oulu team's demo looks promising.
"The use of the smartphone's magnetometer to communicate is very cool," he says, adding that the lack of bandwidth to accommodate all our wireless gadgets means that researchers are always looking for different channels into the phone and this has some promise. "It could be too niche to be broadly applicable – but their demo is novel and exciting," Campbell says.
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