A plurality of active areas are defined on a semiconductor substrate. A circuit board is also rotatably coupled to the fan leaf and electric motor. Optionally provided is one or a plurality of false alarm prevention devices and one or a plurality of enabling switches provided to selectively enable or disable the SERS. When a transaction updates the data item, the optimistic concurrency algorithm ensures that the other instances are notified that the data item has been changed and that it is necessary to read a new instance, from the database or from an updated instance.