The piezoelectric effect is well known and researchers are studying ways to exploit it even better. The latest (that I know of) is an invention by a team at Georgia Tech University.
They have managed to insert a polymer – polyvinylidene difluoride -, a sort of plastic sheet for a lay person, between the two battery electrode. Deformation applied to it by pressure on the battery case generate powers that recharges the battery.
The plastic layer then acts as a nano power generator. The challenge now is to make it produce a significant level of energy, and that can be achieved by including several layers.
By inserting this battery in the bottom of a shoe mechanical energy of the stride is converted into chemical energy in the battery. Notice that the layer of polyvinylidene difluoride convert the mechanical energy directly into chemical energy in the Li-io battery.
In the future we are likely to see a number of these devices embedded in our cloths to leverage the power that is being produced by an activity to produce power in a different form. This is made possible by advances in understanding of materials and by the ever lower energy requirement of electronic chips whose operation can be sustained even by low power, such as the one produced by the piezoelectric effect.