The sensor uses the wireless signal bounced back by a nearby wireless router to power itself up, but there is a snag - since it relies on radio waves the sensor must be 2.5 metres away. While this will make its commercial use a little less practical, the researchers behind the
sensor, "expect to extend this to a meter within a year, and ultimately to 5 meters." The Dutch team are touting the strength of the signal as well, stating it could be applied to walls and surfaces with latex so it could still operate under a layer or paint.
Image credit: University of Technology