A wearable data storage and transmission device and related systems that collect and store sensor data from sensors worn by a user. The device components can include a processor, battery, data storage media, NFC components, Bluetooth components, Wi-Fi components, and wired communications components. The device can remain powered down, powering up periodically to collect sensor data using low energy methods and/or in response to receiving a signal (e.g., NFC, power, Bluetooth, etc.) from an external device that causes the device to power up its components and make sensor data available to the external device. The collected sensor data may be encoded, compressed, stored, and/or exchanged in one or more structured records using various methods to improve the information storage capabilities of the device, including using the disclosed QR coding methods.