COVID Nearby builds on the groundbreaking idea of differential privacy, a mathematical guarantee for your privacy. Differential privacy ensures that the answer to any question is slightly and randomly altered to reduce the risk to your privacy. This risk is controlled by a privacy parameter that enables a trade off between privacy and accuracy. Smaller the value of the parameter, more protected the answers (i.e., more randomize the answer), but with lesser accuracy.
Read more about the privacy-safeguards here.