Smart plug for appliances that plug in, inline relay for lighting you do not want to rewire, smart switch when you are replacing the wall plate anyway. All three do the same fundamental job — switching a circuit remotely — but they differ in installation, appearance and what happens when someone uses the wall switch.
Smart plug
Sits between the wall socket and the appliance. No wiring, no electrician, no permanence.
Use for fans, lamps, chargers, water pumps, anything on a plug.
Watch the current rating. High-draw appliances need a plug rated for the load with margin — do not run a heater through a plug rated barely above its draw.
Bonus — many include energy monitoring, which is the easiest way to find out what is actually consuming power in a home.
Inline relay
A small module that fits inside the wall box behind your existing switch. Nothing changes visually, and the original switch keeps working.
This is the most flexible option and usually the best for lighting. The wall switch behaves normally for anyone who does not care about apps, while schedules and remote control work on top.
Requires enough depth in the wall box and, for most modules, a neutral wire present at the switch. Many older Egyptian installations run only live and switched-live to the switch position, with no neutral.
Check before buying: open the switch plate and look. If there is no neutral, choose a no-neutral module or use smart plugs and bulbs instead.
Smart wall switch
Replaces the whole switch plate with a touch or button panel.
Use when you are already redecorating, or when you want a consistent look across a room.
Consider that it changes the interface for everyone in the house. Touch panels are unfamiliar to guests and older family members, and a panel that needs a firm press in the dark is worse than a rocker switch. Physical-button models avoid most of this.
Load ratings, in plain terms
Every switching device has a maximum current. Exceeding it causes heat, and heat in a wall box is a serious problem rather than an inconvenience.
- Lighting — low draw, almost any module suits.
- Fans and small appliances — comfortably within a standard smart plug.
- Water heaters, pumps, air conditioners — high draw. Use a device explicitly rated for it, with margin, and have it installed properly.
When in doubt, size up. A device running near its limit continuously is the one that fails.
A practical rule
If it plugs in, use a plug. If it is wired and you want the wall switch to keep working, use a relay. If you are changing the plate anyway, use a switch.
See smart switches and SONOFF devices.
Frequently asked questions
How do I know if I have a neutral wire?
Turn off the breaker, open the switch plate and look. Ask an electrician if unsure.
Does a relay work with any switch?
Most work with standard rockers; some need a specific switch type. Check the module's spec.
Can I control a water heater?
Yes, with a device rated for the load and installed properly.