Zoosh. That may or may not be what an ultrasonic payment sounds like to a dolphin, but it is definitely the name of a new mobile wallet technology developed by Silicon Valley start-up, Naratte. While Google and other major players have focused on traditional radio-based NFC, Naratte has been quietly testing its ultrasound system instead, motivated by the fact that it can work on ordinary handsets without the need for specialized NFC circuitry. Two phones can "zoosh" each other using nothing but their built-in microphones and speakers, so long as they're both running the necessary app. Moreover, Naratte claims that cash tills can be upgraded to hear the sweet jangle of ultrasonic cash for just $30 -- around a third of the cost of installing radio-based NFC hardware. So who knows? The last time you came this close to ultrasound was probably just before you were born, but one day you might find yourself using it to buy diapers. Scary.