Could a tag be rendered inoperable if it were introduced into a magnetic or electromagnetic field?
I do not believe that a magnetic field would have much effect on an RFID transponder (if any of our readers have information about this, they are invited to please post it below). However, if you exposed a tag to a strong burst of electromagnetic energy, that would likely blow the circuits in the microchip—just like plugging a radio designed to use 110 volts would be fried if you plugged it into a 220-volt socket—and thus render it inoperable.
—Mark Roberti, Founder and Editor, RFID Journal
Can a Reader Detect That a Tag Has Been Removed? »