Heartbeats can be used to indicate that a unit is alive or to send periodic data. This can be sent out at predefined intervals to indicate that the node is alive, however, it does not necessarily mean the node is functioning as it should. It simply states that the node is connected to the network. To check if a node is functioning, other properties such as a measurement event or registry should be used. This event should be sent as a response to a “Segment Status Heartbeat” (CLASS1.PROTOCOL, Type=1) in order to provide a method of finding out what is connected to the network. The data bytes from byte 3 and forward can be used to send a descriptive/user friendly name if desired.

**Mandatory.** All nodes should send this event at least once each minute. A Level II node should normally not send this event but instead send [Level II node heartbeat](./class2.information.md#type2). Recommended interval is 30-60 seconds but in a node that need to sleep longer to save resources a longer interval can be used.

 | Data byte | Description                                                        | 
 | :---------: | -----------                                                        | 
 | 0         | User specified.                                                    | 
 | 1         | Zone for which event applies to (0-255). 255 is all zones.         | 
 | 2         | Sub-zone for which event applies to (0-255). 255 is all sub-zones. | 
