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Originally Posted by KC Kings
A lot of companies are already using them for supply chain operations. Passive UHF RFID tags are over 20 cents a piece so you can't put them on everything, but you can tag by the pallet and simply drive down the aisle and do a complete inventory in a matter of seconds.
Walmart tried to mandate that all of their products be rfid tagged, but backed out of it because of the cost and difficulty getting a good signal from certain items, such as metal cans.
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Passive tags are effective up to about 3 meters since they don't have their own power supply and simply use the RF energy received from the interrogator to send a response. As Simplex pointed out, unless you have an interrogator every ten feet, it would be useless.
Typical supply chain active RFID tags are roughly 12"x6"x3". Obviously that could be reduced somewhat by eliminating plastic casing. The lithium batteries are good for up to three months, depending on the number of interrogations they go through. Currently, they are effective up to about 100 meters.
The point is, RFID tags are great if you know where the item is, or will be moving it near a known location. An ID chip that is going to constantly broadcast a child's location to a receiver several miles away will need a power source and a robust transmitter.