Using Adafruit's RFID shield, I've just finished installing a system to announce the arrival of frequent visitors by their unique theme song through Adafruit WAV shields placed throughout the house.
For example, my arrival is announced to the Dr. Who. theme song.
Though the system requires visitors to have a Mifare card on them (their company ID badge is usually fine), I'm hoping the new generation of NFC phones will work just as well.
Selecting the theme song for each regular visitor has been an unexpected source of merriment and revelation. Some can come up with an identifying theme song immediately, others struggle with the choice. Not sure what significance, if any, that might have.