The smartphone of the future might lose its sleek, solid shell to become a shape-shifter, able to alter its appearance to signal an alert in situations where visual and audible cues won't do.

Shwetak Patel, a computer science and engineering researcher at the University of Washington in Seattle, and colleagues have developed a squeezable cellphone – SqueezeBlock – using tiny motors built into the casing to mimic the behaviour of a spring.

Pressure plates on the device detect how much force is being applied to the casing, while the motors control the amount of resistance exerted in response. Because the resistance can be tweaked, the degree of squishability can be controlled by some aspect of the phone's status to provide some basic feedback without demanding the attention of eyes or ears.

For example, after the battery is fully charged, the phone might feel as taut as a glutton's post-lunch belly, while a gadget running on empty might be as easy to squeeze as a stress ball. Alternatively, the stiffness could convey the number of emails marked as important that have arrived in a user's inbox.