Smart Plugs: What They're For — and the Loads They Should Never Control

The right mental model

A smart plug is a relay in a box — a small switch, flipped by WiFi instead of your finger, living inside a plastic shell between the wall and your device. Everything about using them well follows from that: relays have contact ratings, contacts wear with every switch cycle, and heat is the enemy of everything in that little box.

For a $12 gadget switching a 60-watt lamp, the engineering margin is enormous — they run for a decade. For the same gadget switching a 1,500-watt heater, the margin is zero, and the failure mode isn't "stops working." It's heat.

What smart plugs are genuinely great at

• Lamps — schedules, sunset automation, away-from-home lived-in looks. This is what they were born for.
• Holiday lights — inside and (with outdoor-rated plugs) outside.
• Fans, humidifiers, aquarium pumps — modest steady loads, well within ratings.
• The anxiety file — coffee maker, curling iron, soldering iron: "did I leave it on?" answered from the driveway.
• Energy monitoring — many mid-range plugs report watts, which is genuinely useful for finding what's eating your bill.

The do-not list

• Space heaters. The worst case on every axis: max continuous draw, thermostat cycling that arc-wears the relay, and consequences measured in fire. Unless the plug is specifically listed for heater duty (a real product category — heavy-duty 15A resistive-rated units from major brands), the answer is no. And the heater-into-wall-outlet rule still applies regardless.
• Anything with a motor that starts under load — compressors, some ACs, sump pumps. Motor inrush hammers relay contacts. (Also: do you want your sump pump's uptime depending on WiFi? You do not.)
• Medical equipment, freezers, security gear — not because of load, but because smart plugs add failure modes (firmware, WiFi, cloud outages) to things that must not fail.
• Extension-cord daisy chains — a smart plug feeding a power strip feeding six things has quietly become a distribution panel made of plastic.

Buying rules from the field

1. UL or ETL listing, verified on the device — not just claimed in the listing photos. The flood of unlisted no-name units is where the melted-plug photos come from.
2. Real brands — the majors have safety engineering departments and recall processes; the $4 units have neither.
3. Match the duty: outdoor loads need outdoor-rated (weather-resistant) units; heavy loads need the heavy-duty category; everything else is standard duty.
4. Feel them occasionally. A smart plug doing light duty runs cool. Warm at the shell means it's working harder than it should — rethink the load or retire the unit.

When the answer is a smart switch instead

If you're putting smart plugs on lamps in every room, or wishing they could control the ceiling fixtures — the graduation path is smart switches in the wall: they handle the full circuit rating, control fixtures properly, and remove the gadget-behind-the-couch clutter. That's a wiring project (neutral wires required for most models — an electrician visit for many older homes), and it's the durable version of what smart plugs are the sketch of.