There are huge range of connected smart home sensors available on the market but many are very expensive for what they actually do and the reliability, accuracy and latency of many of them is questionable. In many cases we have resorted to using the basic electronic components and interfacing them ourselves to get the performance we require and at a significantly lower price.
The advantage of our hybrid technology and technology agnostic approach to our smart home is that we can basically interface and model anything very easily. We therefore have many different types of sensors in our contextual smart home to address a huge range of problems, allowing us to provide the best possible . The use of technology abstraction also allows us our smart home to model and use virtual sensors.
For the best possible performance, our preference is to use wired sensors where ever possible. They also have very low latency. Low latency is good and results in the best possible user experience. With wireless sensors the latency is often visible and also not predictable. This can lead to the smart home misreading the situation because events arrive at the Home Control System in the wrong order. With a hybrid technology smart home this problem becomes more likely.
Wired sensors don't require batteries, so they can be much more responsive and timely. They don't require any kind of battery saving techniques, which result in compromised performance.
Without a doubt wired sensors are also more reliable, assuming the wiring has been installed well. More than 95% of the issues we have had with sensors over the last 14+ years have been with down to the wireless sensors in our home despite there being more than 20 times more wired sensors, than wireless. Wireless technologies are also prone to interference from neighbours, cheap appliances, other technologies and many other factors.
Wired sensors are much more secure, assuming the wires are also physically secure within your home boundaries.
The bottom line though, is that it is not always possible to install wired sensors in your home. It is also a lot more convenient to use wireless sensors than it is to run wires (though good planning during a new build should make wired sensor installation relatively painless). The wireless sensors are going to cause many more issues in use though, so it is wise to consider you options carefully before you start the installation.
Many manufacturers and many consumer buyers take a very 'consumer electronics' approach to smart home, assuming you can just purchase a new one every few years (often even more regularly). There are issues with this approach though. Typically, smart home equipment requires significant integration and configuration effort. The installation process is also not always trivial and some devices are reasonably expected to have a decent lifetime in service.
Wireless technologies come and go. This was one of the reasons we adopted a technology agnostic approach to building our contextual smart home. It makes it much easier to replace technologies as they become obsolete. This is especially true if you have used 'dumb' sensors, with simple wired interfaces and then implemented all the smart features and functions centrally in a Home Control System.
Wireless technologies evolve regularly too and are often not backward compatible. If they are backward compatible, it often results in compromises or reduce performance.
Wired technologies are also potentially prone to being made obsolete but, generally they have a much longer lifetime. We abandoned X10 technology many years ago because it simple didn't work reliably in all parts of our home. Cat5 Ethernet cables installed in our home 10+ years ago are still working perfectly for our smart home needs but in some cases we have pulled through Cat6e cable to replace them (we were wise enough to use conduit/ducting).
The manufacturers of battery powered sensors would often have you believe that they batteries will last for years. And sometimes they may do but, only under perfect conditions. In the real world, the ambient temperature affects battery life significantly. Some sensors are installed in 'high traffic' areas and have to send frequent updates, having a huge impact on their battery life.
Our experience over many years shows that in practice some battery powered sensor batteries can last less than three months before the batteries need replacing. Whilst this might not be an issue if you have just a few sensors, in a smart home like ours with well 400+ sensors, this would results in daily battery changes.
There are a fair number of wireless smart home technologies in use now. Our recommendation is to stick with mesh-network technologies as these provide the best reliability. Typically this includes Z-Wave and ZigBee.
One big issue with wireless sensors is the reporting period. Most use techniques to reduce battery life, which means the last value reported may not now be current. Many can also not be polled to get the latest value. This means they they have limited use in real-time control systems.
In recent times there have been numerous smart home products launched using Wi-Fi. Wi-Fi is not a good wireless networking technology for sensors in the smart home. It is often shared with devices that use much higher bandwidth (e.g. Smartphones streaming video) causing poor reliability and high latency. Wi-Fi is great for some things but is is simple not reliable enough for 'mission critical' smart home applications. Wi-Fi has limitations on the number of devices that can be connected and is subject to many sources of interference.
Wi-Fi is not well suited to battery powered devices as it is very power hungry compared to Z-Wave and ZigBee.
Most sensors need to be installed in the optimum location for the type of sensor. The location often needs to be chosen very carefully and sometimes tested to ensure optimum performance.
Multi-sensors or expensive 'smart' devices containing many sensors inside them are often compromised by their installation location because some of the sensors inside are now not well located for that type of sensor. This is why we avoid multi-sensors wherever possible.
It's a simple fact of life and the smart home that some sensors fail. The challenge in the contextual smart home is to know when sensors have failed and to handle it gracefully. This is good reason to avoid multi-sensors, where one failure can require the whole module to be replaced.
Sometimes sensors lie. There can be many causes of this, both hardware and software. Neither are perfect, software is subject to bugs and hardware is subject to interference.
Sensors that lie can be a problem in the smart home. The trick is to use redundancy for mission critical sensors or to adopt algorithms and strategies to handle the fact that sometimes sensors lie.
Wireless Z-Wave and ZigBee sensors are often very poor at reporting battery life. Many will report less than 100% with new batteries installed. Many also die unexpectedly, even though the battery level reported is more than 80%. Very few wireless sensors report lower battery levels with any kind of accuracy.
There is a good article on this which is worth a read: Forbes - The Internet of Things (IoT): It's The Sensor Data, Stupid.
There are other, more advanced sensors in use in the smart home and we are using cameras, smartphones, tablets and other networked devices as sensors to add to the whole home context in our contextual smart home. More on this to come soon ...
