Mechanisms for tracking an entity are provided. A time is determined by a sensor having a clock, the time being within a time slot in a series of time slots. First data of the time slot is provided and shared between a plurality of sensors. The sensor receives data from the movable entity. The sensor calculates identifying data from the received data for identifying the entity. Derivative identifying data is calculated by applying a modifying function using the provided first data for modifying the identifying data. The sensor calculates a hash value by taking the derivative identifying data as input. The sensor sends a message to a central server for determining the position of the entity, the message comprising the hash value and an identifier of the sensor.