If you have 50 tagged objects on a shelf, and a shelf reader is constantly reading all of those tags, then the system can report when one tagged item is removed. That is, software can be set up to report when a tag is not read for a specified period of time, such as five minutes.
However, it is more difficult to know when a tag is missed. For instance, if you are taking inventory on a rack of clothes, and one tag is not read, because that tag either malfunctions or is blocked by something, then there is no way to know that the item is there but that its tag has not been read.
I should point out, however, that when you are tagging RF-friendly items, such as clothing, plastic totes, paper products and so forth, RFID is generally far more accurate than scanning bar codes. That is, people will miss certain items when using a bar-code scanner, and that number is generally much higher than the number of tags that can not be read. I hope this answers your question.
—Mark Roberti, Founder and Editor, RFID Journal
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