A heartbeat is the simplest form of liveness check. Instead of waiting for meaningful data, the device sends a short “I’m here” message at a fixed interval, and the platform raises an alert when a few are missed. This distinguishes a device that has nothing to report from one that has lost power, dropped off the network or crashed, a distinction that plain telemetry cannot make when readings are sent only on change.
The cost is traffic and energy, which matters on batteries and metered cellular links. Protocols help: MQTT has a keep-alive built into the connection and a Last Will message the broker publishes when a client disappears, which gives the same signal without application-level messages. The interval is a tuning decision: short enough to detect outages usefully, long enough not to dominate the power budget.
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