There are four or five widely used network protocols employed across home automation set ups, each has their own unique set of advantages and disadvantages. Personal circumstance can obviously imapct the utility of each as well, all things considered Zigbee does seem to be the clear winner for the moment, in particular since Amazon, Apple, Google, and the Zigbee Alliance have formed a working group to develop the open standard.
The main protocols currently in use are:
Wi-Fi/Ethernet
Bluetooth & Bluetooth Mesh
Zigbee
Z-Wave
Thread
Obviously there is scope for other protocols such as RF (radio frequency) and infrared however these generally more specialist in use and as such less well supported by the various smart speakers and hubs.
Wi-Fi & Ethernet devices
Pros: Cheap and don't require a seperate hub
Cons: Security concerns, Wi-Fi devices can interfere with your internet connection
Wi-fi capbale devices using the IEEE 802.11 protocol, and their wired brothern on the IEEE 802.3 protocol (Ethernet) are perhaps the most accessible and prevelent devices. These bulbs, switches and plug sockets are generally advertised as Amazon Alexa or Google Home compatible require no specialist hub and can quickly be integrated in to your smart home. Wi-Fi is a little bit of a double-edged sword however, partly due to the security risk of exposing your private network to other devices, and because of the interference that these devices can cause on your network.
Signal strength and Interference
Most modern routers will support 256 devices comfortably without issue so you're unlikely to run into a numerical limit anytime soon, however you are likely to start to see signal interference and drop off in your home as you start to introduce larger numbers of Wi-Fi enabled devices. Unlike other protocols which allow communication via other devices on their network your Wi-Fi range is finite unless you introduce a mesh system or singal extenders.
Security
The other big issues with having Wi-Fi enabled devices is the network that unless you've set up a seperate Wi-Fi network of Virtual Local Area Network (VLAN) for your devices they're attached to the same network as your laptop, shared storage and mobile phone.
If you've performed proper segregation you're unlikely to have any real issues, beyond your lightbulbs being turned on and off until they burn out or the terrifying possibility of your Smart TV being used to spy on you. If you're using your smart devices on the same network as your personal devices such as your mobile phone or laptop however you're opening yourself up to a whole slew of privacy and security concerns. The main issues are:
Single point of failure
In much the same way that you shouldn't use the same password across multiple websites as this increases the likelyhood of one of them being compromised the same logic applies to smart devices. While one unique system may be fairly secure introducing multiple devices increases the liklihood that one of these could be compromised and thus grant access to your wider network.
As devices on your home network are configured to be more sharing and more trusting with each other than they are on an external network such as your local coffee shop a single compromised smart bulb could represent the risk of your financial information, or personal pictures being made accessible to anyone with basic technical know how. By selecting a Wi-Fi that offers a guest network, or allows the creation of a VLAN these devices can be more thoroughtly isolated
Long term support
While it's not to say that all Wi-Fi devices are by default going to be vulnerable a surprising number already are. Unfortunately as in all things if you're lucky you get what you pay for. While TP-Link and Wemo devices are likely to recieve a level of support and security updates for the foreseeable future if only to protect their brand reputation the same is unlikely to be true of a generic £10 S26 (Sonof) or ESP8266 (Tuya). Even on a reputable brand it's to be expected that after a decade or so, as recently discovered by Sonos customers, that security patches are likely to stop. For more generic devices sold at budget under multiple brand names security updates are far less certain. It's for this reason that the the UK government has proposed new security standards.
This is not to say that a better known brand is always a better option, Wemo has previously had a number of security warnings, Philips Hue likewise has been shown to be vulnerable to hacking but simply point out that you're likely to get considerably less support on cheaper more generic devices. Regardless of what you're spending you should always think about isolating your devices.
A lot of platforms and hubs support both Zigbee and Z-Wave such as Smartthings and Hubitat.
Zigbee
Pros: large range of inexpensive devices from a variety of suppliers, including cheaper Chinese market versions, can support 65,000+ devices on Mesh network
Cons: Requires a smart hub, shorter (but more extendable) range than Z-Wave, possible Wi-Fi interference
Zigbee is a wireless protocol which operates in a mesh network and is generally the standard at this point in time. Being embraced by a large number of devices such as Ikea's Tradfi line, Philips Hue, Samsung SmartThings and Yale it's also as mentioned above been chosen as the base for a new open standard.
Interference, range and speed
As Zigbee operates at 2.4 GHz it runs the risk of intefering with your Wi-Fi signal, this high frequency means Zigbee can transmit more data, but also reduces the range of the signal to around 10-20 metres (33-66 feet). This is somewhat offset by an increased hopping distance compared to Z-Wave, put simply you can cover a greater distance but only if the devices are closer together
Security
Both Zigbee and Z-Wave use the same AES-128 symmetric encryption so neither has an edge. While Silicon Labs kept Z-Wave as a propriatary protocol, Zigbee being open source held the edge here, however in response to Project Connected Home over IP (CHoIP) Z-Wave is being open sourced in the second half of 2020. So the real question from a security point of view comes down to the hub used rather than the devices themselves.
Hubs & Availability
Zigbee, like Bluetooth, RF or Z-Wave devices all connect to a hub or 'bridge' rather than directly to the internet so are useless until you commit to a platform. A number of options exist here from SmartThings, to Hubitat and in house only solutions such as Zigbee2mqtt.
The real beauty of the zigbee network is that being open most of the devices are inter-compatible which means you can buy cheaper zigbee devices from the Chinese market and use them in the UK without any of the security issues that would be associated with similar Wi-Fi enabled devices.
Z-Wave
Pros: Fantastic range, no risk of Wi-Fi interference
Cons: Generally more expensive, Capped at 232 devices
Z-Wave is very similar to zigbee in that both are Mesh networks, however Z-Wave using a (historically) proprietary protocol represents more of a security risk, and due to lower competition generally higher prices.
Interference, range and speed
Z-Wave uses a much lower 918/960 MHz frequency making it unlikely to interfere with other devices and offering much better range 30 metres vs an upperlimit of 20 metres for Zigbee. Newer devices can go much further. This lower frequency does mean devices are slower, but not to a noteworthy degree.
Security
As a general rule of thumb open standards are more secure than closed ones, as every secret creates a potential failure point. Open systems being subject to more scrutiny are more likely to be identified and patched. While Z-Wave remains proprietary it may be subject to more flaws however as your attacker is more likely to remotely target your hub than come into range of your property to try to interfere with your Z-Wave devices this is more a question for your smart hub than your bulbs or plugs.
Bluetooth and Bluetooth Mesh
Pros: Potentially huge range, (some) backwards compatibity
Cons: There are virtually no commerical devices available yet
Bluetooth devices are for obvious reasons pretty universal, and while they traditionally lack the range of other solution the Bluetooth Mesh specification released in July 2017 overcomes these. While Alibaba is one of the players backing Bluetooth Mesh so far the availability off devices in the UK is non-existant beyond tile style tracking devices.
Thread
Pros: Huge possibility, a potentially better mesh network than Z-Wave or Zigbee
Cons: There are virtually no commerical devices available yet, limited to 250 devices
Much like Zigbee and Z-Wave, Thread connects your devices together using a mesh network. Unlike Zigbee and Z-Wave, Thread doesn't require a hub to connect them and is thus "self-healing". Virtually any Wi-Fi or Zigbee device could be upgraded to use Thread with only a software update as it leverages the 802.15.4 protocol.
Unfortunately Thread only appears in a few Nest devices so looks likely to be a dead end.
MQTT
Pros: Can be managed internally, working without external access
Cons: lacks any encryption out of the box, a single compromised device could monitor all network traffic openly
Message Queuing Telemetry Transport or MQTT is a commonly used protocol within a number of the open sourced home hubs, being particularly useful for those looking to create a smart system that doesn't require an active internet connection. However it can also be used for numerous external systems and forms the basis of much of SmartThings Home Assistant integration. As with all other formats it requires either internet accessible devices, or a specialised hub to connect to your existing network, though mqtttozigbee and mqtttozwave controllers are now readily available.
Security
From a security standpoint the unencrypted nature of mqtt is a concern, as any compromised device on the network could gain full access to all data being shared. While encryption is possible this would fall to the end user. Ultimately how much of a concern this is rather down to the security of your home network and router.
Choosing a network
Ultimately, whatever protocol you decide to adopt will, to a point, dictate what devices you can use moving forward and so is worthy of consideration. However if you're willing to adopt multiple hubs around your house then most Smart Home set ups will interlink a range of protocols either using external or internal network solutions. While devices may claim to be compatible with Apple, Amazon's Alexa or Google Assistant this generally involves either a bridging device such as a Philips hue or SmartThings hub, or means communicating with a server halfway around the world. Smart devices can exist in isolation, controlled only via an app or via a smart speaker but home automation requires integration, and for now the biggest names seem to be looking at Zigbee.
FAQ
What is a mesh network?
A mesh network is a mesh created by numerous devices using the same protocol allowing direct, dynamic and non-hierarchical connections between devices. One of the primary limiting factor of devices for home automation is their range, Bluetooth, Zigbee and Z-Wave solutions are limited by walls and distance, allowing devices to act like repeaters for each other extends their range. Think the 101 Dalmations 'Twilight Bark' or 'Lighting of the Beacons' in Lord of the Rings.
Is Alexa Zigbee Compatible?
No Alexa is not directly Zigbee compatible. However Alexa can communicate with a number of smart hubs using the Zigbee protocol, and via these bubs control Zigbee devices.
Is Google Assistant Zigbee Compatible?
No Google Hub is presently Zigbee compatible. However Google Assistant can communicate with a number of smart hubs using the Zigbee protocol, and via these bubs control Zigbee devices.
Is Alexa Z-Wave Compatible?
No Alexa is not directly Z-Wave compatible. However Alexa can communicate with a number of smart hubs using the Z-Wave protocol, and via these bubs control Z-Wave devices.
Is Google Assistant Z-Wave Compatible?
No Google Hub is presently Z-Wave compatible. However Google Assistant can communicate with a number of smart hubs using the Z-Wave protocol, and via these bubs control Z-Wave devices.
Zigbee Vs. Z-Wave
It is generally used across a large number of devices and platforms many zigbee devices also support Z-Wave and vice versa the one real problem with it historically was that Z-Wave Proprietary protocol that means that it has certain security concerns because it's not open and can't be properly audited
Devices that work with Zigbee
Some well known smart home brands and devices that support Zigbee (otherwise known as Zigbee certified products) include:
Philips Hue
Samsung SmartThings
Amazon Echo Plus (with Alexa for voice controls)
Hive Active Heating and accessories
Honeywell thermostats
Ikea Tradfri
Belkin WeMo Link
Yale smart locks
Sengled smart lights
ADT Security Hub
Wink hub
Somfy blinds and drapery motors
GE Appliances
LG SmartThinq
Lux Konoz
Devices that work with Z-Wave
Many big name brands also support the Z-Wave standard – and you can see all the certified products on the official website. Here are some of the highlights:
Samsung SmartThings
Wink hub
Honeywell thermostats
Hogar Milo (with Google Assistant for voice controls)
ADT Security Hub
August smart locks
Yale smart locks
Logitech Home Harmony Hub Extender
Somfy
GE Appliances
LG SmartThinq
Kwikset smart locks
*An extensive report on the status and sutability of the various protocols used for the Internet of Things and home automations is out with the scope of this article, and as such protocols such as X10, and KNX will not be discussed. This is not to dismiss the utility of these systems but rather because these are generally older and heavily geared towards home automation enthusiast who already understand the topic to a great depth. This article instead will be covering off the main protocols currently being used and the various implications behind these within the standard home automation setups.