NOVID: Anonymous Contact Tracing with Ultrasound

Last updated on 14 May, 2020

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Anonymously and reliably trace your exposure to COVID-19 to keep yourself and others healthy.

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The hunt for viable solutions to help stop the spread of the COVID-19 pandemic now occupies the minds of almost every single profession. From engineers to mathematicians, and even to clothing brands who now make masks, everyone wants to do their part in stopping the spread. Po-Shen Loh, a Carnegie Mellon University math professor, is no different. He realized back in March that, with a combination of math and physics, he could develop a digital solution to stop the spread of COVID-19. The key initial insight was that COVID-19 spread uncontrollably because people infected others before they even felt the slightest bit sick, and his research area of network theory could be a game changer in pandemic response.

NOVID is the product of two months of sleepless nights and passionate efforts of a group of around 20 individuals, many of whom are alumni and students of Carnegie Mellon University. They ultimately created the first anonymous contact tracing app published in the USA for both Android and iOS which did not collect any personal information (no GPS, phone number, email, name, etc).

Under the hood, what sets NOVID apart from other contact tracing applications is its use of ultrasonic technology to augment the wireless communication properties of Bluetooth. Many other proposed apps rely only on Bluetooth, but those signals pass through walls and ceilings in apartments and offices. Consequently, Bluetooth-only solutions have the dangerous potential of falsely detecting invalid contacts who had no way of transmitting the disease.

Indeed, for ordinary applications the range of Bluetooth is an asset, but this technology does not produce precise short-range distance measurements. Other apps measure and record the received signal strength indicator (RSSI) corresponding to nearby devices, but they do not immediately calculate distance because it is still an unsolved problem to reliably translate RSSI into precise distance, especially in complex environments with obstacles that absorb the signal. Contact tracing is a very sensitive task which needs to be carefully executed, and thus the technology that people put in their pockets needs to be accurate. By leveraging ultrasonic technology, NOVID has developed a simple protocol which employs the physics of sound to accurately gauge distances between devices, with minimal impact on battery, and maximum privacy. 

NOVID uses the physics of sound to achieve far better precision than Bluetooth or GPS solutions, drastically reducing inaccurate detection. Sound travels at about 343 meters per second. If Device A sends a sound out at Time X, and Device B hears that sound at Time Y, the distance between them is a very simple calculation: Distance = Rate × Time, or 343 × (Time Y − Time X). Of course, if people are close by, we are talking about milliseconds of difference between Time Y and Time X. NOVID has been successfully able to measure these differences.

While using NOVID, the user's mobile device will emit an inaudible sound, a fraction of a second long, in the frequency range of 18–20 KHz. When two devices communicate, they are able to identify the distance of said interaction, and store it in their own local databases. Since the application is specifically programmed to work on these high frequencies, it will never process sounds even remotely close to the human voice frequency band. NOVID does not use GPS tracking, which means that all interactions are simply recorded on a relative distance basis, rather than on an absolute location basis. Instead of sensing that Device X and Device Y were both at Location Z, NOVID senses that the devices were simply Distance W from each other. To alert people who might have been infected by others, all that is needed is relative distance, not absolute location. The beauty of collecting only distance measurements is that they avoid recording or storing any location data, which is inherently non-private. (Your typical location at 3 a.m. indicates a lot about you.)

To ensure privacy, each user is only assigned a randomly generated ID at install time, rather than a username. Without any personal details, the app then sends random temporary ID’s to nearby devices, which they record as interactions. When an ill user self-reports an anonymous positive COVID-19 test, we process all of that person's prior interactions, and then send out anonymized alerts to all of the possibly exposed users. NOVID was founded by a network theory expert, and as such, employs efficient network algorithms to be able to not only alert people to first-order (direct contact) exposures, but also second-order, and even third-order connections to the virus.

The user experience of the application has always been at the forefront of NOVID. As much as contact tracing is a technical challenge, it is first-and-foremost a social challenge. Without a good user experience, the technical capabilities will not fulfill their potential, and vice-versa. NOVID allows users to view informative interaction metrics displayed on the dashboard; information empowers users to take control of their actions, in a time where we have very little control over the world around us.

The dashboard has three main purposes: self-reporting, daily interaction metrics, and possible exposure alerts. The Self-Report section allows users to report whether or not they have tested positive for COVID-19. The Daily Interactions section features a chart that displays how many unique interactions a user has had each day over the past week, along with how many of those interactions lasted more than 15 minutes. Finally, the Possible Exposures section displays possible transmission events between users, broken down by the aforementioned degrees of contact: direct contact, indirect contact, and distant contact. 

Empowering users to know when they’ve had exposures allows them to make informed choices about social distancing, thus protecting the rest of their community from further exposures. NOVID is beyond just a contact tracing application—it is a movement towards a safer global reopening.

NOVID is currently available for download on both the iOS and Android App stores. Please download to help Stop the Spread.