1. https://venturebeat.com/2011/06/19/narattes-zoosh-enables-nfc-with-just-a-speaker-and-microphone/. https://venturebeat.com/2011/06/19/narattes-zoosh-enables-nfc-with-just-a-speaker-and-microphone/. Accessed: 2020-03-13. https://venturebeat.com/2011/06/19/narattes-zoosh-enables-nfc-with-just-a-speaker-and-microphone/. https://venturebeat.com/2011/06/19/narattes-zoosh-enables-nfc-with-just-a-speaker-and-microphone/. Accessed: 2020-03-13.
2. Ultrasound detector android app. https://play.google.com/store/apps/details?id=com.microcadsystems.serge.ultrasounddetector&hl=en. Accessed: 2020-03-13. Ultrasound detector android app. https://play.google.com/store/apps/details?id=com.microcadsystems.serge.ultrasounddetector&hl=en. Accessed: 2020-03-13.
3. SurroundSense
4. PinDr0p