Track your pets, children, cars without having to worry about the tracker's battery life.
Imagine a pet collar with a built-in GPS device and a mobile sim card. The device would be charged via a micro kinetic charger powered by your pet's movement. Such kinetic chargers are used in some watches.
The kinetic charger would be able to very slowly but surely charge the device. Every now and then the battery would fill up sufficiently to power up the device and send off the pet's GPS location then go back into hibernation. If the pet was lost the owner would simply wait for the location message and quickly go there.
In kidnapping prone areas such devices could be built into your children's shoes/clothing. Likewise for cars, motorbikes, and so on.