13: Heartbeat

A message sent to let the receiver know the sender is still active/alive. Can also be used to check if a connection is still active, as the message should be ACKed. Devices currently default to sending a heartbeat every 15 seconds on open links. Arbitrary fields can be added in fields payload 200+

Payload

Field	Name	Description	Type	Unit
6	Battery Percent	Devices send battery percentage in heartbeats	uint8

Examples

Basic

The most basic heartbeat to keep a connection active. It has no header fields and no payload fields.

Including battery %

Devices will automatically add battery % to heartbeats

📡 Real example from RH2 P1 v2287 on 2025-10-09This example is captured from an RH2 device as part of normal communications over I2C with the ESP32 co-processor

With message ID 2456632031

Message IDs can be added to heartbeats to increase traceability, but they are not required

📡 Real example from RH2 ESP32 Toit on 2025-10-10This example is captured from an RH2 device, where Toit on the ESP32 co-processor is sending a heartbeat to the RH2 over I2C

With arbitrary data in payload field 202

If you are sending a heartbeat between systems you control You can add arbitrary data in payload fields 200 and above, Such as these additional bytes, which are "hello" in ascii.

Code

For convenience, the following constants can be used to reference this message type.