I find the (short) video easiest to follow:
Best of all, it is incentive-compatible. The founder Po-Shen Loh, a mathematician from Carnegie Mellon, wrote to me:
…for each positive case, don’t just ask the direct contacts to quarantine; instead, tell everyone how many relationships away COVID just struck (e.g., “3” is a contact of a contact of a contact). Then animate this over time like a weather radar…Keep everything anonymous.
Suddenly, the main purpose of the intervention is no longer to protect others from you (quarantining after being exposed). Instead, it is to directly protect you from others, because that early warning of approaching COVID lets you know it’s a good time to wear a better mask, or to be more vigilant about distancing, because the situation is getting hot. This appeals to self-protection instincts instead of altruistic instincts. Since this app is already in deployment, we know anecdotally, for example, of a person who installed the app because his kid was going to a university that was using the app. Why? So that he could be alerted in case COVID started spreading his way from the university via his kid.
Here is his associated preprint. As economists, ought we not to feel that appealing to self-interest and love of family sometimes works?