Can an unpowered 2.4 GHz transceiver exist?
It's probably passively powered.  RFID tags can have processors that are powered entirely by the energy derived from the RF signal used to query the tag.  The tag/processor combo can only function when the RF signal is present or if it stores energy from the RF signal then as long as that lasts.  Otherwise it just shuts down.  Typically it transmits its unique ID and possibly a small amount of other data.