Researchers at King Abdullah University of Science and Technology in Saudi Arabia have developed a low-cost mechanism that makes it possible to destroy a telephone remotely to prevent others from gaining access to confidential data.
 
This mechanism is based on a polymer layer that can expand seven times larger when heated beyond 80°C. The material is composed of microspheres containing a hydrocarbon that transforms from liquid to gas when heated.
 
This mechanism can be activated remotely or triggered automatically when pressure is applied on the device (attempts to open the casing) or it is removed from a restricted area and geolocated by GPS.

Source : http://www.techniques-ingenieur.fr/actualite/articles/autodestruction-smartphone-solution-radicale-41970/