A system is provided for sensing blood glucose data of a patient. The system includes a sensor, user interface, and an optional auxiliary device. If the connection between the sensor and user interface is by a wire, the sensor remains powered when the wire is disconnected. The communication between the sensor and the user interface may be wireless. The auxiliary device can be a patient monitor or other display or signal device, which displays information about the blood glucose data collected by the sensor. The sensor is connected to sensor electronics, which include a sensor power supply, a voltage regulator, and optionally a memory and processor.