Our method was straightforward. Venues could generate a random 15-digit number for a QR code using open-source software. Visitors didn’t need an app; they simply scanned the QR code and sent a SMS to a secure number, 1922, containing only the random number. This process allowed venues to verify participation without learning personal information, such as phone numbers. The telecom companies storing these numbers were also unaware of the locations these numbers corresponded to, retaining the data for about 28 days. In the event of community transmission, we could efficiently issue exposure notifications to those who visited the same locations.