Systems and methods for generating and using ephemeral identifiers are provided. One example method includes determining, by one or more computing devices, a current time-count. The method includes determining, by the one or more computing devices, a time-modified identifier based at least in part on a static identifier and the current time-count. The method includes determining, by the one or more computing devices, an ephemeral identifier based at least in part on the time-modified identifier and a rotation key. One example system includes a plurality of beacon devices, at least one observing entity, and at least one verifying entity.