The power flickers for half a second, and a smart home reveals its assumptions. The router comes back, the televisions forget their settings, and the smart plugs each make a private decision about what to do next. Some turn on. Some stay off. Some restore whatever state they held, and one in the garage reboots into a state that no automation accounts for. Power-restore behaviour is one of the oldest specifications in the switchgear industry and one of the least-read lines in a smart plug's datasheet, and it decides what a five-second outage costs.
Why the Decision Exists at All
A relay has no memory; the firmware does. At boot, the plug must choose: always on, always off, or restore the last state before power was lost. Each choice is correct somewhere. A lamp the family toggles with the app wants last-state, so the outage is invisible. A pump that must not run unattended wants off, so a blackout does not restart it into a dry sump. A freezer or a server wants on, unconditionally, because its whole reason for being plugged in is continuity.
The trouble is that manufacturers pick a default for the average customer and rarely surface the setting. Plugs that boot to on are common because the demo is better: nobody at a trade show watches a plug stay dark. The buyer discovers the default during the first outage, at the exact moment when nobody is reading the manual, and the consequences range from a blinking clock to a basement full of meltwater.
The Failures a Boot Choice Causes
Boot-to-on turns outages into hazards for anything that must not start unattended: heaters, irons, hotplates, power tools left plugged in. A device that was safely off when the power failed is running when the power returns, hours later, to an empty house. Boot-to-off does the opposite damage to anything that must keep running: freezers, sump pumps, aquarium heaters, medical equipment. The plug that stayed dark through the outage keeps it dark afterwards.
Neither default is wrong. What is wrong is not choosing. The setting exists in most competent firmware, sometimes in the app, sometimes behind a long-press on the button, sometimes documented nowhere. Before a plug is assigned to a load that matters, the boot behaviour should be tested with the plug's own button: yank the power mid-state, restore it, and see what happens. Thirty seconds of empirical testing beats any datasheet.
The Rest of the Boot Sequence
Power-restore is the visible decision, but the boot sequence has more corners. How long does the plug take to join the network after power returns: a plug that reconnects in seconds re-enters the automations smoothly; one that takes minutes leaves scenes half-executed and schedules ambiguous. Does the relay click on before the radio joins, meaning the load runs before the network can intervene. Does the plug preserve its schedules and timers through the reboot, or resume from a firmware default that has not been edited since installation.
Brownouts are the sneaky case. A sag, not a cut, can reset a plug's microcontroller without interrupting the relay, leaving a device that reports one state while its radio is wedged. Firmware that handles brownout detection cleanly is worth more than the marketing suggests, because brownouts are more common than outages and produce the strangest support tickets.
Generators and the Transfer Case
Buildings with backup power add a variant worth planning for. When the transfer switch moves the house to generator power, the delivery is not utility-clean: frequency and voltage wobble during the transition, and cheap electronics reboot in cascades. A smart plug that boots to on during a transfer may start loads the generator cannot carry simultaneously, tripping the circuit that was supposed to hold the house together. Load priorities in an outage are an electrical design question, and plug boot behaviour is one of its inputs.
The mirrored case matters too: when utility power returns, the same cascading reboot happens in reverse, and every plug that boots to on presents its load at once. Utilities call this cold load pickup, and it is why a street's lights blink twice after a storm.
What to Standardize On
Fleets and projects need a policy, not a per-plug discovery process. Assign boot behaviour by load class: continuity loads boot to on, hazard loads boot to off, convenience loads boot to last-state. Document which plug model holds which default, because a mixed fleet with inconsistent firmware defaults is an outage waiting to be misunderstood. And test the policy annually with a controlled power cut: unplug the switch, watch what comes back, and compare it to the plan.
Questions Before You Standardize
The questions are about the boot sequence, not the amperage. What the power-restore default is for each model, and whether it is user-configurable in the app. Whether the setting is enforced in firmware or lost on re-pairing. How long reconnection takes, and whether schedules survive. Whether brownouts are detected and handled. What the vendor's own fleet policy is, if they deploy their own products, because a manufacturer who runs their own fleet has answers the datasheet never needed until now.
A plug family that answers these treats power events as a first-class case. A family that boots everything to on and moves on treats the outage as somebody else's problem. The difference is invisible in a working building and decides, during the first flicker, whether the smart home rides through or wakes up confused.
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