COVID Alert DE works by using random Bluetooth keys that change every 10-20 minutes. Phones with the app installed will share these random keys anonymously if they are in close proximity. Positive COVID-19 results submitted by other app users are checked against the list of random keys they have encountered in the past few days. If there is a match, COVID Alert DE alerts the individual, taking into account the date and duration of the exposure, and the Bluetooth signal strength, which is used to estimate proximity.