Is it possible, using a contactless Near Field Communication (NFC) reader, to determine if a tag is still there after a certain span of time?
Yes. With any passive RFID reader, the device continually communicates with a tag. If the tag is removed, it no longer responds. Readers can be set up to indicate when a tag no longer responds, and to transmit that information to a back-end system.
—Mark Roberti, Founder and Editor, RFID Journal