Apparatus and methods for blood analyte sensing, data processing, and transmission and storage. In one embodiment, the sensor comprises a spatially compact multi-element implantable blood glucose sensor apparatus which is configured to generate signals or data relating to sensed blood glucose levels of a host being, and process the data in vivo to generate e.g., data suitable for transmission to an external receiver device for storage and indication. The implanted sensor apparatus may also determine the need for an alert. In one variant, the sensor apparatus provides for ultra-low energy consumption through a number of coordinated mechanisms, including only issuing wireless transmissions (advertisements) when communication is needed, and use of multiple “layered” operating modes. Reduced energy consumption advantageously also extends implantation longevity and reliability/availability.
