A mechanism for authenticating a physiological sensor is disclosed. When a sensor is connected to a monitor, the monitor examines whether a first sensor-specific usage identifier of the connected sensor is consistent with a second sensor-specific usage identifier thereof. The first and second sensor-specific usage identifiers are indicative of the cumulative usage of the connected sensor, but may nevertheless be unequal. The first sensor-specific usage identifier is maintained in the sensor and the second sensor-specific usage identifier in a host memory external to the sensor. The use of the connected sensor is allowed when the examining indicates that the said two identifiers of the connected sensor are consistent, and rejected when the identifiers are inconsistent. The two identifiers are further updated in response to the use of the connected sensor in the patient monitor, thereby to keep the said identifiers consistent and updated for a subsequent use attempt of the sensor.
