Are Smart Plugs Safe to Leave on All the Time? — Complete Guide (2026)

Yes, certified smart plugs are safe to leave plugged in and powered on 24/7. Smart plugs that carry UL (Underwriters Laboratories) or ETL (Intertek) certification have been tested for continuous operation, heat resistance, and electrical safety. They draw approximately 0.5-1.0 watts in standby mode and are designed for always-on use. The key safety requirements are buying from reputable brands with proper certification, never exceeding the plug’s maximum load rating (typically 1,800 watts or 15 amps), and avoiding certain high-risk appliances like space heaters and high-draw devices. When used correctly, a quality smart plug is no less safe than any other certified electrical device in your home.

Safety Certifications: What to Look For

Not all smart plugs are built to the same standard. The single most important factor in smart plug safety is whether the device carries a recognized safety certification mark. Here is what to look for and what these certifications actually mean:

UL Listed (Underwriters Laboratories) — This is the gold standard in the US. A UL-listed smart plug has been independently tested for electrical safety, fire resistance, overheating protection, and build quality. The testing includes running the plug at maximum rated load for extended periods and verifying that internal temperatures stay within safe limits.

ETL Listed (Intertek) — ETL certification is equivalent to UL in terms of rigor and is recognized by all US and Canadian authorities having jurisdiction. Many brands use ETL instead of UL because Intertek often has faster certification timelines.

FCC Certified — This is required for any wireless device sold in the US and verifies that the smart plug’s radio does not cause harmful interference. It is separate from electrical safety certification.

What to avoid: products with only a CE mark (European standard, self-declared by the manufacturer), no certification marks at all, or suspicious-looking marks that mimic UL or ETL but are not actual certifications. Cheap smart plugs from unknown brands on marketplace sites sometimes use fake certification marks or list certifications they do not actually hold. Check the UL or ETL online databases if you are unsure — you can search by product or manufacturer.

Reputable brands like TP-Link Kasa, Meross, Wemo, and Eve all carry proper UL or ETL listing on their smart plugs.

Maximum Load Ratings and Why They Matter

Every smart plug has a maximum wattage or amperage rating, and exceeding it is the primary way smart plugs become unsafe. Most standard smart plugs are rated for 15 amps at 120 volts, which equals 1,800 watts. Some compact or mini-style plugs are rated lower at 10 amps (1,200 watts).

Here is a reference table for common household devices and their typical wattage:

• Table lamp: 10-60 watts (safe)
• Floor fan: 50-100 watts (safe)
• Television: 80-200 watts (safe)
• Coffee maker: 600-1,200 watts (safe, but check rating)
• Slow cooker: 200-300 watts (safe)
• Window air conditioner: 500-1,500 watts (check specific unit)
• Microwave: 1,000-1,500 watts (near max, not recommended)
• Space heater: 1,000-1,500 watts (not recommended)
• Hair dryer: 1,000-1,875 watts (exceeds most ratings)
• Toaster oven: 1,200-1,800 watts (at or above max rating)

The general rule: if an appliance draws more than 1,000 watts, think carefully before using it with a smart plug. While a 1,200-watt coffee maker is technically within the 1,800-watt rating, sustained loads above 60-70% of maximum capacity generate more heat in the relay and wiring. Devices that cycle on and off at high wattages (like space heaters with thermostats) create repeated thermal stress.

Smart plugs with energy monitoring, like the TP-Link Kasa EP25, are particularly valuable because they show you exactly how many watts each connected device draws. If the reading shows you are near the plug’s maximum, move that appliance to a direct wall outlet.

Devices You Should Never Plug Into a Smart Plug

While most household devices are fine with smart plugs, certain appliances should always be connected directly to a wall outlet:

Space heaters. This is the most important one. Space heaters draw high sustained wattage, generate significant heat themselves, and are already the leading cause of home heating fires. Adding a relay-based smart plug into the power path introduces an additional failure point. Most space heater manufacturers and fire safety organizations explicitly warn against using any extension cord, power strip, or intermediate device including smart plugs.

High-wattage kitchen appliances. Toaster ovens, air fryers, and large microwaves operate near or at the maximum rating of most smart plugs. The sustained high draw can overheat the plug’s internal relay over time.

Motorized high-draw appliances. Portable air conditioners, large dehumidifiers, and shop vacuums can have inrush currents (the initial surge when the motor starts) that exceed the smart plug’s rating even if the running wattage is within range. This inrush can damage the relay.

Medical equipment. CPAP machines, oxygen concentrators, and other medical devices should always be connected directly to a wall outlet. A smart plug firmware glitch, Wi-Fi dropout, or accidental routine trigger could disconnect power to a critical device.

Anything with a heating element above 1,000 watts. This includes irons, clothes steamers, and electric griddles. Heating elements draw constant high wattage with no rest cycles.

The devices that are perfect for smart plugs: lamps, fans, phone chargers, TVs, game consoles, sound systems, humidifiers (cool mist), holiday lights, and coffee makers (standard drip models under 1,000 watts).

How Energy Monitoring Improves Safety

Smart plugs with built-in energy monitoring add a meaningful layer of safety beyond simple on/off control. These plugs measure the real-time wattage, voltage, and current of whatever is connected to them, giving you visibility into how your devices are performing electrically.

Here is how energy monitoring helps with safety:

Detect failing appliances. An appliance that suddenly starts drawing 20% more wattage than normal may have a developing electrical fault. Energy monitoring smart plugs can alert you to these changes before they become dangerous.

Verify you are within ratings. You may not know exactly how many watts your coffee maker draws. A monitoring plug shows you the real number so you can confirm it is well within the plug’s 1,800-watt limit.

Track cumulative costs. Energy monitoring reveals how much each plugged-in device actually costs you to run, helping you make informed decisions about usage patterns and whether certain devices need replacing with more efficient models.

Set automatic shutoffs. Some smart plug apps let you set a wattage threshold trigger. If the connected device suddenly exceeds a set wattage limit, the plug automatically cuts power. This is a meaningful safety feature for appliances that could malfunction.

The TP-Link Kasa EP25 is one of the most popular energy-monitoring smart plugs, priced around $13 with accurate real-time wattage reporting and historical usage tracking directly in the Kasa app.

What We Recommend

For safe, reliable, always-on smart plug use, we recommend the TP-Link Kasa EP25. It carries ETL certification, includes energy monitoring to verify device loads and track electricity costs, supports Matter for cross-platform compatibility, and costs around $13 per plug. It is rated for 15 amps (1,800 watts), and its compact design does not block the adjacent outlet. Stick with its published ratings, avoid plugging in space heaters or high-wattage heating appliances, and you can confidently leave it powered on around the clock for years without concern. The standby power draw of about 1 watt costs less than $1.50 per year, making the safety and convenience of a quality smart plug well worth the negligible energy cost.