We embed marketing tools in ultrasound signals and decode it with the app to trigger the desired action, like notifications, a welcome message, a coupon, tickets, maps, etc, all offline. We can also synchronize all the smartphone in events and turn the pixels into spectacular light shows by broadcasting the signals through the sound system of sport stadiums, music events, retail or conferences. NFCSound is an ultrasound barcode that can be encoded into a unique audio stream. Any device with a speaker can transmit it and most devices with a microphone can decode them. Can complement existing networking technologies or to work in offline environments. NFCSound does not require to go through any server and the encoding take place in the device self.