Smart Plug vs. Switch vs. Relay?

 

If you are new to the smart home scene and have done a little YouTube or other web browsing, you might be asking why would I use a smart switch or smart relay instead of the simple smart plug.  Read on, or watch my YouTube video, for more info on when you might select a particular device over another in your smart home.

Smart plug, smart switch or smart relay?

If you are a newbie or an experienced home automation aficionado, odds are that some of your first devices were simple smart plugs.   These devices come in a variety of shapes and sizes and have various features, including energy monitoring on some models.  While smart plugs are some of the easiest devices to install and configure, in some instances they may not be the right choice for a particular home automation.

For example, consider the following scenario:

You have a lamp controlled by a wall switch.  But you'd like to make this lamp "smart" so that it can be controlled via your home automation platform.  You might do this so the light can come on at sunset and go off at sunrise... or automation can assure the lamp is turned off when no one is at home. So, the simplest solution is to configure a smart plug, plug it into the switch-controlled outlet and plug the lamp into the smart switch:

But this presents a number of problems.  What happens when the wall switch is turned off?  Power is now cut to the smart switch and it will no longer respond to automation or other control commands.  Similarly, if the smart plug is turned off, flipping the wall switch will have no impact on the lamp.  Your inclination might be to do this:

PLEASE DON'T DO THIS!  Especially if you live with others in your household.  You are probably just going to frustrate your housemates.  Remember that "smart" functionality should always enhance or add to existing functionality of a device, and never remove basic functionality.  Instead, consider the use of a smart switch in this situation:

Now you still have the same basic functionality of standard switch control, but have also added the ability to control the lamp via automation.  Yes, you are going to have to shut off the power and do a little basic wiring (only do this if you are comfortable working with household wiring. Be sure to shut off the appropriate breaker and follow the switch installation instructions. If unsure or uncomfortable, consider hiring a qualified electrician).  You could also potentially add a smart dimmer switch, adding additional functionality with a dimming option where there wasn't this option before.  Just be sure the device/bulb you are connecting supports dimming.  Not all LED bulbs play nice with dimmers!

But one potential drawback with a switch is that most smart switches come in a 'decora' format... as opposed to the normal single pole switch that you may be replacing.  And this might be an issue if you are replacing a single switch in a panel that looks something like this:

In this case, you'd have to find or order a new faceplate to accommodate three "normal" switches and the smart switch "decora" style.  So you'd have to find a faceplate that looks something like this:

And this becomes more difficult (but not impossible) if the 'smart switch' is one of the inner switches.  Or maybe you or your significant other don't like the decora look and prefer to keep the look of a standard switch.  This is where the smart relay comes into play:

A smart relay can be installed behind your existing standard single pole switch and convert that switch into a smart switch.  From the exterior, everything looks exactly the same... and the wall switch functions exactly like it did before.  But again, like with a smart switch, you can now add automation to the switch (and anything connected to that switch).  In addition, smart switches are a bit bulky and in situations where you have multiple other switches/circuits in the same box.  A smart relay might fit better in the box.  The Shelly line of smart relays (shown above) are about the size of two stacked Oreo cookies.  Yes, this is going to take a bit more wiring than a switch, but the instructions are easy to follow.

A note about neutral wires:  Nearly all smart switches and relays require the presence of a neutral wire in the box.  There are some smart switch options that do not require a neutral (Lutron is one example), but check your intended destination for the presence of a neutral wire before making your purchase.

Home Automation Integration and Custom Firmware

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Of course you need to make sure the particular plug, switch or relay you choose is compatible with your home automation platform... or that it can be flashed with custom firmware such as Tasmota, which both frees the device from the cloud or manufacturer's app and makes it compatible with systems like Home Assistant.  Home Assistant maintains a list of officially supported device integrations. Additional integrations can also be found in the Home Assistant Community Store (HACS).

If considering the custom firmware route, be aware that in the not-to-distant past, most plugs, switches and relays used the ESP8266 chip that was easy and straight forward to flash... sometimes even over-the-air without disassembly or soldering.  But recently, many manufacturers have begun changing the chipset and flashing is no longer possible (or very difficult).  There is a list of supported devices for Tasmota on Blakadder's site.  Note that things can change rapidly and some devices are easier to flash than others.  For example, most smart plugs are glued together and there is a high risk of damaging or destroying the plug in an attempt to open it for flashing.  For smart plugs, I would recommend the Sonoff S31 series.  These plugs can be easily taken apart (just a snap off cover and three small screws) and the pads for flashing are easily accessible.  For a video on how to flash a Sonoff plug, I'd recommend watching Digiblur's YouTube video, where he flashes a Sonoff S31 with no soldering.

For wall switches, as of the time of publishing, the Gosund switches were still able to be flashed with Tasmota, but this may change at any time.

For relays, it's hard to beat the Shelly line of relays.  Not only do the Shelly relays provide pin headers for flashing, without disassembly or soldering, but now have MQTT built-in, so it is possible to integrate into most automation platforms without any custom firmware.

Finally, a company called Athom sells a number of plugs, switches and relays pre-flashed with Tasmota, giving you the custom firmware without the need to disassemble and flash the device yourself. 

How to decide?

Whether a plug, switch or relay is the best choice will highly depend upon the end use and personal preference.  While a plug will always be the easiest to install, the use case may be better served by a switch or relay, even though the latter two take a little more effort to install.  Think through your intended purpose, potential current and future automation desires and don't forget to take other household members into account and both the "approval factor" and ease-of-use.  Then do your research to assure compatibility with your home automation platform (or the ability to install custom firmware) before making any purchases.

 

Let me know in the comments if you have any additional thoughts or questions!