# 3.x Heartbeat The sensors periodically send their data through all channels they can: this is known as sensor heartbeat. The sensors try broadcast the data, if GATT is connected the sensor data is sent via GATT and NFC data field is updated to include the latest data. On GATT the data is sent via Nordic UART Service TX Characteristic notifications. Bluetooth advertisements have the data encoded in Manufacturer Specific payload. NFC has the data as a binary in field utf-8 field with language "dt". The heartbeat also feeds the watchdog of the application, if the data updates stop for any reason the application assumes that it has crashed and reboots. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.ruuvi.com/ruuvi-firmware/3.x/3.x-heartbeat.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.