All smart devices need a way of communicating with other devices. That’s central to what makes it smart. There are two broad categories for connecting a device, wired and wireless connections.
Wired connections are great for a number of reasons. They are simple, reliable, and typically very secure. They aren’t susceptible to interference, and the system is expandable without degrading performance.
Ethernet & Power over Ethernet (PoE):
Ethernet is the gold standard for networked equipment for good reason. It is widely adopted and has been standardized for decades. Power over Ethernet (PoE) has been a standard for well over a decade, and has been in wide use in enterprise ever since, allowing low power devices to be powered over the same cable as data. One cable for everything.
In a hypothetical ideal smart home, most devices would be wired and powered over Ethernet. Basically the only compromise you have to make when using Ethernet is in deployment. Wires are hard to install unless you are doing new construction, and the current housing stock has very little deployed structured wiring. For this reason, by the numbers, it isn’t popular, despite the clear advantages.
If you are building new, run Ethernet for everything. Eventually everything will go that route. It’s too popular in the enterprise/business space to never make the jump to residential eventually. It’s simply too convenient.
Low Voltage/Security Wiring:
Low voltage wiring is the other type of wiring a modern house will contain for data, mostly in alarm system applications, or for some types of sensors or indicators. Again, this is the way to go when building new, otherwise wireless is going to end up the more popular choice for alarm systems. It’s just a radically cheaper install in existing buildings.
All wireless data connections are based off radio technology. There are many different schemes and frequencies used to accomplish this. Wireless devices are susceptible to interference, require batteries, and can’t scale infinitely, but man to they install quick and simple! That’s basically the feature that makes them super popular, especially for existing buildings.
Using 2.4ghz and/or 5.0ghz, IEEE 802.11, otherwise known as WiFi to everyone is the most common wireless protocol in use today. It’s a open standard and many devices use WiFi as their data connection since all it requires is it’s own chip and a wireless network to connect to for data service. Building a device with WiFi makes setup simple for consumers, especially those already familiar with adding devices to their network. It is a very popular choice for Smart Device manufacturers, especially for one-off devices that aren’t meant to be in a system of many dozens of devices.
Z-Wave is the winning protocol from the early days of Home automation specific wireless protocols. It runs at ~900mhz, which gives it better range and signal penetration characteristics vs Wifi. It’s designed for low power usage, mesh connections between devices, and uses an RF frequency that doesn’t interfere with normal WiFi signals. Many Home automation devices are built around Z-Wave. It does require a device to act as a hub to control all the devices in the network, and it’s ease of use and utility is pretty much dictated by how well designed that hub is. Two homes with the exact same set of sensors and devices but different Z-wave hubs could have a radically different user experience.
Zigbee is like Z-wave, but run at the same 2.4ghz frequency as WiFi. Because of this crucial difference, professionals have mostly opted for Z-wave instead, which has a longer range and doesn’t interfere with normal WiFi. There are still a number of products that exist for Zigbee. I wouldn’t recommend using Zigbee unless you already have lots of it and are thus already committed to it in part.
Wireless Security Sensors
Alarm systems use either generic or proprietary protocols, generally down in the 300-450mhz range. There is a push to start encrypting these sensors and devices for security against hacks. In general the control panel/alarm board will communicate with all the devices, and getting a data connection to the panel is what you worry about in terms of a data connection for the alarm system. Because these sensors tend to be proprietary, it’s often harder to change systems down the road, as it’s not a simple one item swap out like a wired alarm panel would be. Wireless is just popular because it’s easy.
Insteon is a curious system that is a mix of wired and wireless. The language spoken between devices is all the same, but connection methods can differ. It’s a combination of Power-line communication & Z-wave like wireless sensors. Some devices even come with both modes in a dual-path configuration for extra reliability.
On paper, it is the most advanced option for home automation, and grew out of the X10 protocol, the original professional grade home automation protocol from the 90s. It has a robust history of long term support Z-wave can’t match.
It is also, like Ethernet, infinitely extensible. The main advantage Z-wave has over Insteon is market penetration. Insteon was slow out of the gate with products people actually wanted, and have been playing catch up ever since. These days you can find a Insteon version of pretty much any smart home device, and it is a technically superior platform. It would be my choice building new, at least for things like lights, power outlets, switches, etc.