We can no longer function without our digital devices. We have smartphones in our pockets and tablets shoved into our purses and backpacks. Even our homes are becoming automated, letting us control our Internet of Things devices from anywhere, whether from the car, the office or halfway across the continent.
But as our homes become "smarter," we're seeing a number of competing wireless-network standards. These include not only the familiar Wi-Fi and Bluetooth, but others such as Thread, WeMo, ZigBee and Z-Wave. What are the differences among these new standards? Can they coexist in the same household or office?
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What a Smart Home Needs
The ideal smart-home gadget would use a wireless transmitter and receiver that required very little power, so that devices could go for months, or even years, without needing a new battery. Its signals would pass through walls and floors inside and outside a home, yet without interfering with other wireless networks.
Signals would be encrypted for security reasons, and the user would be able to easily add devices to the network. All devices on the same network would be able to "talk" to each other. Finally, the standard should be able to handle dozens or even hundreds of devices on a single network.
Standard Wi-Fi consumes a lot of power, so it doesn't quite fit the bill. Bluetooth Low Energy (LE) is better at conserving power, but is limited in both signal range and number of devices (the new Bluetooth mesh standard, however, could fix some of these issues).
Most of these new standards create decentralized "mesh" networks in which each device can communicate directly with any other device within range. If two devices are too far apart, their signals can hop along intermediate devices. Devices can drop in and out of the network without affecting the network's overall strength.
However, most of these networks also need a "primary" device that serves as a network controller. If the primary device drops out of service, another device can often take over. Interfaces with smartphones or tablets can be handled by hubs, commercially available devices that are often compatible with two or more of these standards, as well as with Wi-Fi or Bluetooth. Two of the leading hubs, Samsung SmartThings and the Wink 2, can not only receive Zigbee, Z-Wave, Bluetooth, and Wi-Fi, but also let you link smart devices together, so that one will activate when another meets certain conditions.
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How They Compare
| Row 0 - Cell 0 | Z-Wave | ZigBee | WeMo | Thread | Bluetooth mesh |
| Operating range | 100 feet | 35 feet | 100 feet | 100 feet (theoretical) | 330 feet |
| Max no. devices | 232 | 65,000 | Router-dependent | 250-300 | 32,000 |
| Data rate | 9.6-100 kbps | 40-250 kbps | Router-dependent | 250 kbps | 1 Mbps |
| Frequency | 908/916 MHz (U.S.) | 915 MHz/2.4 GHz | 2.4 GHz | 2.4 GHz | 2.4 GHz |
| Network type | Mesh | Mesh | Star | Mesh | Mesh |
| Needs hub? | Yes | Yes | No | Yes | Yes |
Z-Wave
Along with ZigBee, Z-Wave is one of the most widely used wireless standards in smart homes today. The Z-Wave Alliance cites more than 1,300 certified devices on the market and 35 million compatible units sold.
"ZigBee and Z-Wave have been out there for years," Kerber said, explaining that each protocol defines all the network functions of all compatible devices to ensure maximum compatibility with other devices running that protocol. "All service providers that provide a smartphone solution use ZigBee and Z-Wave because of interoperability."
Both Z-Wave and ZigBee use AES-128 symmetric encryption, the same as offered by some online banks, to safeguard communications, and devices using either standard are easy to set up and don't require the consumer to perform any wiring.
Large brands such as Honeywell use Z-Wave, as do home-security-device companies ADT and First Alert. Other customers include AT&T, Jasco (maker of GE-branded home products), LG and Verizon.
Despite their similarities, ZigBee and Z-Wave are not compatible with each other. From the consumer's point of view, it's hard to pick one over the other, though each protocol's proponents would beg to differ.
"Z-Wave is the only technology on the market to deliver applications-level interoperability and maintain backwards compatibility across all versions," said Ben Garcia, Z-Wave field applications engineer for Sigma Designs, the California-based company that owns and licenses the Z-Wave standard. "When something is Z-Wave certified, it will work with any other Z-Wave product, past, present and future."
Z-Wave products include a number of smart locks (which also have Zigbee), as well as the GoControl garage door opener. Because Z-Wave uses a low-frequency radio band — 908.4 MHz in the United States — its devices will not interfere with a Wi-Fi network, though they might with cordless landline telephones.
Z-Wave has "better interoperability, historically, than Zigbee," said Michael Wolf, founder and chief analyst of NextMarket Insights, a strategy and research firm in Edmonds, Washington. "All Z-Wave devices generally, without exception, work with other Z-Wave devices."
Sigma Designs makes money licensing Z-Wave, and devices using the standard can be pricier than those using other protocols. Like DVDs, Z-Wave devices can't be used outside their "home" regions due to different radio frequencies — for example, North American Z-Wave devices won't connect to Australian ones.
Z-Wave is also relatively slow, with data-transmission rates of up to 100 kilobits per second (kbps). By comparison, its competitor ZigBee can get up to 250 kbps at certain wavelengths, while the latest version of Wi-Fi, which draws much more power than either ZigBee or Z-Wave, can reach 1 gigabit per second — 1 million kbps.
ZigBee
Unlike the proprietary Z-Wave standard, ZigBee is an open standard based on the IEEE 802.15.4 wireless-data specification. ZigBee device makers include GE Appliances and Lighting, LG, Logitech, Philips Hue lights and Samsung. (Some of these manufacturers also use Z-Wave, Bluetooth or Wi-Fi.) ZigBee is also used by Comcast and Time Warner Cable in their set-top boxes, as well as in home-gateway routers and satellite receivers, and the familiar Nest Learning thermostat. Amazon even incorporated Zigbee into its newest Alexa smart speaker, the Echo Plus.
ZigBee can work on the 915 MHz frequency in the United States, which allows for low-power consumption but limits data to 40 kbps, or on the 2.4 GHz frequency, which allows for up to 250 kbps but might interfere with Wi-Fi networks. ZigBee products include the Philips Hue smart light bulb, the Logitech Harmony Ultimate home-control hub, motion detectors built by Bosch and Indesit washing machines.
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"It works well when all devices are using the same Zigbee profile," Wolf said. "[It's] cheap and very low-power, and the mesh technology is perfect for home automation."
ZigBee also supports battery-powered devices, some of which can operate up to seven years on one set of batteries, and devices that don't have batteries, such as light switches.
ZigBee is reliable and "robust," said Ryan Maley, director of strategic marketing for the ZigBee Alliance — it's low-power, interoperable with other ZigBee devices and secure.
"Wi-Fi is the appropriate choice to deliver content like streaming video and audio. It's great for the Internet of people," Maley said. "ZigBee is designed for devices talking to devices. It's great for the Internet of Things."
Because the two protocols communicate differently, ZigBee and Z-Wave devices are often incompatible. However, many smart-home hubs, such as Lowe's Iris, Quirky's Wink hub, and Samsung SmartThings support both protocols, although they may not say so on their packaging.
"Historically, Zigbee's suffered from interoperability issues with various implementations using different software profiles," Wolf said. "They appear to have this under control."
As noted above, ZigBee is somewhat faster that Z-Wave, and is generally cheaper to implement for device makers. However, ZigBee has a range of only 10 meters (35 feet) whereas Z-Wave can reach 30 meters (100 feet).
WeMo
Next we have WeMo, which is a brand owned by Belkin, a maker of networking gear and tech accessories, and not a wireless networking standard at all. Instead, WeMo piggybacks on standard Wi-Fi, already ubiquitous in networked homes, which removes the need for a hub or controller and also makes its devices Internet-compatible. WeMo devices send signals through a Wi-Fi router to each other, to the larger Wi-Fi local network and to the Internet as a whole.
Peter Taylor, director of product management at Belkin, said the company chose to use Wi-Fi because it didn't want to confuse customers by "introducing other technologies."
Instead of a mesh network, WeMo is dependent on the "star" network configuration common in most home Wi-Fi setups, with a central router handling all the traffic among devices and controlling the network in general. Because the user's smartphone is already on Wi-Fi, he or she can install the WeMo app to interface directly with WeMo devices.
But there's a drawback to Wi-Fi — it takes up a lot of battery life and processing power.
"Wi-Fi is much more power-hungry than other wireless technologies for the home," Wolf said. "Battery-operated smart-home devices are a terrible choice for Wi-Fi."
Head to the Belkin Home Automation website, and you'll see more than 25 WeMo products, such as the WeMo LED Lighting Starter Set, the WeMo Insight Switch and the WeMo Switch + Motion set. WeMo also partners with brands such as Mr. Coffee and CrockPot to add its networking technology into those devices.
"WeMo is app-based, so devices that have a WeMo app can connect to it like a phone or tablet," he explained. "Other devices that use WeMo can also connect to other WeMo devices to talk and communicate."
One example would be to have a WeMo motion detector trigger other WeMo devices when the user walks through the front door. The Amazon Echo can work with WeMo products as well. So how does WeMo fit within the diverse smart-home-automation industry?
"We are very aware of the other standards out there, as well as the different alliances and consortiums vying to create new ones," Taylor said. "We agree with the mission of these groups and will move in the direction of adopting the winning standard whenever that may occur, but we haven't aligned ourselves with any group or standard as of yet."
Not all Wi-Fi-based smart-home devices can "talk" to WeMo devices. For example, the SmartThings Hub, supports the WeMo Light Switch, Motion and Switch, but not the WeMo Insight switch. (The SmartThings Hub also supports ZigBee and Z-Wave devices.)
Thread
First announced in July 2014, Thread is coming about because Google's Nest Labs, Samsung Electronics, ARM and others wanted a smart-home networking protocol that could support the Internet of Things for years to come. Thread is an open wireless protocol that natively handles IPv6 (the next generation of Internet Protocol addressing) and, like ZigBee, is based on the 802.15.4 radio standard. (Thread does not handle the older, but more commonly used, IPv4 Internet address standard.)
"One thing about ZigBee and Z-Wave is that they're not IP-based," Kerber said, and hence can't easily work with Internet Protocol-based standards such as Wi-Fi, Ethernet or 4G LTE.
"There's an adaptation layer that matches IPv6 to the lower layers" of otherwise non-IP smart-home networking standards, Kerber said, "and that's called 6LoWPAN. Thread is based on that."
Thread will work with the Nest Learning Thermostat and the Nest Protect smoke detector, both produced by Google, as well as with Brillo, the stripped-down embedded version of Android for Internet of Things devices announced by Google in May 2015. (Brillo will also work with Wi-Fi and Bluetooth LE.) However, Thread won't with the Nest Cam, formerly known as the Dropcam, as the camera lacks the necessary 802.15.4 chip.
"Thread supports battery-operated devices as part of a home network," said Chris Boross, president of the Thread Group. "This allows the devices that people use every day — including thermostats, lighting controls, safety and security products — to be a part of the network without requiring constant charging or frequent battery changes."
The Google connection could be a drawback, however.
"Many manufacturers are resistant to use a new technology that is based on Google/Nest [intellectual property]," Wolf said.
The protocol creates a self-healing low-power mesh network that can link more than 250 devices, and Boross said Thread closes security holes found in other wireless protocols. It uses radio communications in the 2.4 GHz band, which might interfere with Wi-Fi signals.
Because ZigBee and Thread share basic physical specifications, it's likely that future software modifications, such as the already-mentioned 6LoWPAN, would create some degree of interoperability between the two standards.
"Thread and ZigBee have announced that the two organizations are collaborating to enable the ZigBee Cluster Library [application protocol] to run over Thread networks," Boross said, implying that Thread could probably handle ZigBee devices, though maybe not the other way around.
Bluetooth Mesh
First announced in July 2017, Bluetooth mesh builds upon the Bluetooth Low Energy standard, and will allow devices to communicate with each other in a distributed network, much in the same way that Zigbee and Z-Wave devices do. While it has a much longer range—up to 300 feet, under ideal circumstances—its low transmission rate will keep it from being used for data-heavy applications such as video.
By virtue of its ubiquity, Bluetooth mesh has the potential to be as big a player as ZigBee or Z-Wave, though it's far too early to make an accurate prediction. It should be able to work with any device that has Bluetooth 4.0 LE, though adoption depends on whether or not device makers release an update for their gadgets.
Are They Secure?
How secure is all of this technology? Mika Ståhlberg, director of strategic threat research at Finnish antivirus firm F-Secure, said most Internet of Things devices transmit encrypted data.
"Your data is sent directly to the cloud, or first via ZigBee, Z-Wave or similar, to a smart-home hub, and then to the cloud," Ståhlberg said. "You then access this data and send commands to your devices with a mobile application, and you use, e.g., your Facebook account to register the application to the cloud service."
It's possible that a hacker could steal a password to retrieve personal data or manipulate a device. He could also hack the cloud backend of that service, or gain access to device data through physical access. There's a low chance that someone would take the time to hack the low-power radio traffic within a home, but there's still plenty of room for human error.
"As scary as it is, it currently seems your password will replace your house key," Ståhlberg said. "And we know how good people and services are with keeping passwords safe."
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Right now, most Internet-of-Things hackers hijack home routers, set-top-boxes and network-attached storage devices not for the personal data they contain, but for their computing power, which can be used to mine bitcoins, send spam and crack passwords. And most smart-home device use processors that are too weak to be used for those purposes.
"We expect that this trend will continue for a few years more," Ståhlberg said.
But he thinks that as smart-home devices become more powerful, and the personal data they contain becomes more valuable, they may become targets as well.
"As homes become smarter, attacks that target the home and its inhabitants directly are becoming more probable," he said.
What's to Come
From a consumer's point of view, it doesn't matter much which smart-home wireless standard to select, especially since ZigBee and Z-Wave are virtually identical in terms of functionality, WeMo is limited to one brand, Bluetooth Mesh is just starting, and Thread hasn't yet gotten off the ground.
The best thing to do might be to decide which smart-home devices you want, then to see how many of them are available on one standard or another. Fortunately, many brands of smart-home networking hubs are already compatible with two or more of these standards.
Will there ever be one standard to rule them all? Only time will tell. As more devices enter the room and consumers vote with their wallets to create winners and losers, it's possible that we will see a shakeout that will lead to only one or two smart-home wireless standards.
Kerber, however, notes that ZigBee and Z-Wave have had 10 years to build up alliances and certify devices, with the result that there are thousands of compatible devices on the market between them. He thinks both they, and their newer competitors, will be around for some time.
"I still think it's going to be another 10 years before we see any consolidation," Kerber said.
