Smart Plugs and Energy Monitors: Find What Is Using Your Electricity

You cannot cut what you cannot see. Smart plugs and plug-in energy monitors are inexpensive devices that show how much individual appliances use, helping you decide where to focus your efforts. They are among the simplest smart-home tools for saving energy.

Plug-in energy monitors

A plug-in monitor sits between the wall socket and the appliance and shows the power drawn in watts, the energy used in kWh and often the cost, if you enter your unit rate. They are cheap, simple and independent of Wi-Fi. Leave one on a fridge or freezer for a few days and you will see its real average use, not the label figure.

Smart plugs

A smart plug lets you switch an appliance on or off remotely or on a schedule, using an app or a voice assistant. Many models also measure energy use. They are useful for lamps, heaters and devices that you want to run only at certain times. Do not use a smart plug with devices that should not be switched off unattended, such as medical equipment, or ones that are not rated for the power load.

What to measure first

Fridges and freezers, especially old ones, to see whether replacement could save money.
Entertainment centres, where TVs, boxes and consoles can draw power even when off.
Computers and work equipment left on overnight.
Portable heaters, dehumidifiers and tumble dryers, which draw a lot of power when running.
Chargers and standby devices that add up across the home.

Using the results

Record the watts when the appliance is on and in standby.
Estimate hours of use per day or week.
Calculate the energy and cost with our appliance cost calculator or the formula in our guide to appliance running costs.
Decide whether to switch off, replace or change habits.

Safety

Check the maximum load of the plug, which is commonly 13 amps or about 3,000 watts. Do not exceed it.
Buy from reputable brands, and look for UK safety marks.
Do not daisy-chain extension leads and adaptors.
Do not use smart plugs for unattended heating appliances unless designed for it.

Smart plugs and privacy

Many smart plugs connect to the internet through an app. Choose brands with a clear privacy policy, keep firmware up to date and use a strong, unique password for the account.

Understanding standby power

Standby power is the electricity a device draws when it appears to be off or idle, such as a television on a red light, a games console in rest mode or a charger left in the wall. Each device may use only a watt or a few watts, but they run all day, every day. Measure the standby draw with a monitor, multiply the watts by the 8,760 hours in a year and divide by 1,000 to get kWh, then multiply by your unit rate to see the annual cost. Switching off the worst offenders at the wall, or putting a group of devices on one switched socket, is a simple habit that costs nothing.

Is it worth it?

A low-cost monitor often pays for itself by finding a single wasteful device. If you have a smart meter, the in-home display gives an overview, as described in our smart meter guide, and a plug-level monitor tells you which appliance is responsible.