The Sensi Wi-Fi Thermostat, made by HVAC veteran Emerson, is one of the more basic and affordable smart thermostats commonly available today and offers integration with Apple HomeKit, Amazon Alexa, and Google Home (no IFTTT or Cortana at present). Like all smart thermostats, the Sensi allows control both on the unit itself and via smartphones or smart speakers, including flexible schedules and geofencing (which can change thermostat settings when one or more people move outside a 3-mile radius). It's a large, low-profile rectangular unit with a non-touch screen and four rather cheap hardware buttons: mode, menu, up, and down. However, Wi-Fi connectivity means that one never actually needs to press these buttons after one very quick step during setup. For sighted-types, the LCD display lights up to show temperature, time, and indoor humidity, and a setting allows the display to optionally stay lit permanently as a sort of night light. An optional inexpensive wall plate adds an approximately three-quarter-inch border around the unit and adds to the look of the plain white box, as well as hiding any jagged sheet rock or screw holes from the old thermostat. Below, I discuss installation, accessibility, and home assistant integration.
Although a blind person cannot install a thermostat independently, the process is usually straight-forward for an average home-owner and so can be done with sight assistance. The thermostat is connected to the furnace via a bundle of 18-gauge low voltage wires that attach to a 24-volt alternating current transformer. Obviously, disconnect power to the air handler before touching these wires to avoid damaging the unit. The wires are color-coded to help ensure that the terminals on the thermostat match their equivalents on the furnace. The coding is conventional but not a requirement. So, although the fan wire is often green and connects to the "G" terminal, for example, don't count on it. For this reason, thermostat instructions will almost always suggest taking a picture of how your existing thermostat wiring looks to lower the chances of getting confused.
Installing a thermostat is a simple process of 1) pulling the thermostat off its base, which is the only part screwed to the wall, then 2) moving the colored wires from the termonals on the old thermostat back plate to the same terminals on the new one. Then screw the new thermostat plate onto the wall and stick the unit itself onto this base.
If old and new terminals are the same, then it is essentially that simple. However, older thermostats typically did not have the power requirements of wi-fi connected units, and there's an all-important "common wire" terminal that may be unconnected on your old thermostat. If so, pull the wire bundle out from the wall a few inches and see if there are unused wires. The "C" wire is often blue, but again, this is a convention rather than a requirement. If you have an extra wire, this can be connected to the "C" terminal on the new thermostat to supply constant power. You will have to connect the same wire to the "C" terminal on the back of your furnace. If the wire bundle lacks a suitable wire, then a new wire will need to be run--either a C wire kit or a whole new bundle of wires. If, like me, your system is in the attic, it's very likely time to call a pro to fish the wire down from the attic to the thermostat. So, although thermostat installation can be simple if all the connections exist, it becomes worth the $70 to $100 to have an HVAC technician or handyman install it if running new wire is involved.
The Sensi Wi-Fi thermostat can operate on two AA batteries without a C wire, making it more flexible than most other smart thermostats, but HomeKit functionality does require C wire connection. In my case, my wire bundle had a blue wire my technician could use.
The Sensi IOS app start screen has a button for "install thermostat," which launches a very straight-forward guide that provides both step-by-step information better than that found in the printed guide, plus sets up the thermostat and integrates it with HomeKit. One screen of this process requires sight assistance, since the user must tap images of all the terminals that your thermostat utilizes. This step is how the app knows what type of system you have. The process could have been made accessible, but it is not. On another step, the user must see the code displayed on the thermostat screen. In short, keep a sighted person handy and run the app while installing the hardware.
One thing that surprised me was that the app seemed to grab my wi-fi information and feed it to the thermostat without any user intervention at all. I was never asked for a wi-fi password or to do any of the steps required for, say, and Echo or Google Home device.
The Sensi app is only partially accessible. At the time of writing, setting up schedules is not possible for a blind person, and the "About" screen does not provide any information accessibly. Buttons are intelligible but not labeled well. I have also not been able to set the heat and cool targets within the app. I can access the current ambient temperature, mode, and humidity level, change heat/cooling/auto mode and fan mode, and I can adjust important system settings like preventing short-cycling or changing from Fahrenheit to Celsius.
Fortunately, HomeKit does allow automations with the thermostat, and I would probably prefer using HomeKit to create my schedules in any case. Between the partially-accessible Sensi app and HomeKit or Alexa, then, all functions are usable without much inconvenience.
Adjusting the set point control within the Home app, however, is tricky. Once the thermostat is part of your existing home, which is usually done during initial thermostat setup, navigate to the accessory and set the rotor on "Actions." Choose "adjust controls" to adjust the mode and set point. The temperature control is an up/down slider, but simply using the "adjust value" setting on the rotor moves the set point in unpredictable ways. Instead, tap and hold the slider control, then move your finger up and down by very small amounts. Adjusting the temperature in this way by only one or two degrees requires dexterity. When creating a schedule under the HomeKit Automations tab, adjusting the set point in this way is the only option I know.
HomeKit, Alexa, and Google Home
For day-to-day monitoring and adjustment, Siri, Google Home, and Alexa are the best ways to use the thermostat. Unfortunately, the vocabulary for issuing commands is different for each platform, and phrasing must often be precise, particularly for Alexa. For example, asking Siri "What is my home's temperature?" will return the thermostat ambient temperature reading, but saying the same thing to Alexa will provide local weather conditions. The Alexa phrase is "What is the thermostat temperature" or "what is the temperature on my thermostat." Both devices respond to "Set the thermostat to 74 degrees" or, to get the set point, "what is my thermostat set to." Similarly, if the thermostat is assigned to the room "hallway," you can say "what's the temperature in the hallway?" Using one of these AI assistants is the easiest way to use the thermostat. At the time of writing, neither Alexa nor HomeKit provide access to the humidity sensor. Google Home does, however. These things change rapidly. When the manual was written, for example, there wasn't a Google Home Sensi service yet. Note that use of the Apple Home app outside the home, as always, does require set up with either an Apple TV or an IPad running in Home Hub mode.
Despite accessibility issues with the app, the deep HomeKit integration for scheduling, readout, and control make the Sensi a good option for a blind person seeking an accessible thermostat. I tend to doubt that prices will fall much further for this technology. Competitors with touch screens, like Sensi's own touch version of this product or the fancier Nest and EcoBee, are less accessible due to the lack of hardware buttons, and their added sensors or learning capabilities may not be needed by those of us with simple homes. Another option to consider is the equivalently-priced Honeywell Lyric T5, which lacks AA batteries but offers roughly the same feature set as the Sensi, but it does have a touch screen.
Honewell's more expensive "Lyric Round Thermostat" has a glass dial and touch-sensitive buttons. I was happy to see smart thermostats hit the $100 pricepoint. Ten years ago, I payed twice as much for the VIP-1000 talking thermostat, which died after a couple of years. Its demise made me happy, because it was too verbose for my tastes, announcing a lot of extraneous information and doing so both slowly and too loudly. I replaced it with a cheap, tactile, non-programmable thermostat that served just fine; a quick notch on the dial with my Swiss Army knife allowed me to turn it to my desired heat or cooling targets. For a moderate price, though, I was happy to add this new type of accessible thermostat to the cadre of smart plugs that power my sound system, computer, and lights.