How to Track Vampires, Space Aliens, Shoes and Wasps: if you're going to track all these with the same gadget, then you'll need something small. Here is the world's smallest RFID (radio frequency Identification) device. Not long ago, they were finger-sized. Now, they're mote-in-you-eye sized. The article explains the technology and shows photographs of some mote-in-your-eye RFID devices made by Hitachi.

Wal-Mart put the price pressure on RFID technology years ago by demanding that pallets of inventory arrive at stores with RFID tags, so that the pallets can be easily identified for content and location. Expensive inventory with legs (such as expensive shoes) can be easily tracked. A customer can be tracked as well, to learn his/her buying habits. There are many other uses, including the ones SF writers will imagine.