Wake-on-LAN only works from inside the LAN — so I put a $5 ESP32 on the LAN. It subscribes to an MQTT topic and broadcasts magic packets on demand. The build, the failure modes, and what a hardware watchdog is really for.
A powered-off machine has no OS, no IP stack, no running software — yet a single crafted broadcast frame boots it. How the NIC stays half-awake watching for its own MAC, why WoL is a layer-2 trick, and the homelab plumbing to make it reliable.
A superloop is the right architecture more often than embedded tutorials admit — until the day it isn't, and you need preemption, priorities, and blocking. What FreeRTOS actually buys you on an ESP32, and what it costs.
MQTT moves a temperature reading in about 30 bytes over a connection that survives flaky cellular links and sleepy microcontrollers. The publish/subscribe model, the three QoS levels, and the retained-message and last-will tricks that make it click.