Currently rate this product at a 4, been in service a couple of months now, purchased with a total of 5 external sensors. The occupancy sensing and wireless/zigbee sensor aspect is really a leg up over competitors such as Nest and Honeywell. Operation is somewhat quirky: It uses a weird averaging algorithm between sensors which applies greater weight to occupied areas than unoccupied. I would have expected the system only use occupied areas. The algorithm seems to result in some unpredictable behavior when weightings change, sometime resulting in a short off-cycle with calls for heat (say 3min)...for some reason this drove my furnace bananas until they suggested a hack where you apply a minimum ventilation cycle. If it were me, I'd set it up with a simple minimum off-time parameter similar to the cool off recycle time setting they have for heat pump systems.
The system is not a pure occupancy-based solution, you still need to set schedules. I would prefer pure occupancy where the sensors drive home or away settings without time clocks. Further to that, the system will not go into 'smart away' (vacant) mode until TWO HOURS have elapsed with a lack of motion detected on all sensors. Yet another reason this gets 4 stars.

I spent a long time comparing both the Ecobee3 and the Nest thermostats. What finally sold me on the Ecobee was the remote sensor feature. It only makes sense that a thermostat not only know the temperature of its installed location but also of the entire house. I plan to buy more sensors because I placed my single sensor upstairs. The Ecobee does an amazing job of making our home comfortable. And now that the price has been reduced, it made me pull the trigger. Installation was easy and everything worked out of the box. Thank you Ecobee!

This review will focus on two areas of the Ecobee that I feel customers should really be aware of: (1) Review of it while it's working and (2) What to expect when you must call Customer Service if it breaks.

Firstly: For the period between November 2, 2016 and January 8, 2017, the Ecobee and the "bees" we purchased with it worked wonderfully. The temperature was stable and the Ecobee worked well with our newly installed 2-stage furnace. The interface is clean, responsive, easy-to-use. Even our HVAC technician was interested in learning more about it given how excited we were and how we talked up its potential. Operationally, the Ecobee worked well. HOWEVER...

Today it experienced a failure and I was forced to call Ecobee's Customer Service to troubleshoot. In under 90 days of use, the item broke. It read the temperature in my house as -6F and was running the heater non-stop to raise the temperature. It would not let us shut it down, but when we did, it would recover intermittently with error messages related to humidity and temperature.

I'd like to talk about the experience you will have if you are forced to call customer service and why I feel Ecobee has a ways to go to catch up with other HVAC and home automation options with respect to troubleshooting and customer care.

Do not call Ecobee unless you have a voltrometer, the presence of your HVAC professional, jeweler's screwdrivers, a smartphone with a camera, three people, and an email. Not many homeowners have a voltrometer on hand, so be sure to pick one up while you are buying a space heater at Home Depot. I know you have a C wire, but if you threw away the box with the power jumper that was included with the box (because you didn't need it), you should probably hang up and fire up that space heater.

We had to call twice because of missing requirements (the voltrometer and our HVAC professional). A total of 2 hours and 25 minutes were spent on the phone with Ecobee customer support.

Be prepared to spend 50 minutes on hold before your call is answered. Then be prepared to spend an additional 90 minutes troubleshooting your installation, wiring, and system. Despite mounting evidence that the issue is with the unit itself, the Customer Service rep was forced to have us perform new and sillier resolutions. Our HVAC guy determined it was the Ecobee in under 20 minutes, but thankfully stayed around while we made the call and saved us from vague instructions. He remarked that there was a potential to short the circuit board on our new heater if we weren't careful with the remediation requests (i.e. shutting off power before switching wires). The Customer Service Rep provided those instructions in the wrong order when relaying them to us. The HVAC professional also noted two troubleshooting instructions that were redundant based on the numbers from the voltrometer. It's safe to say he won't be recommending this unit to his customers based on what he heard over the phone and that's unfortunate because it's a very nice unit.

After approximately 90 minutes on the phone, the Customer Service rep requested the following photographic evidence:
(1) A picture of the wiring at the device
(2) A picture of the Voltrometer measuring the wires and in spec. That took three people to complete. (Did he not believe us when we gave the measurement over the phone?)
(3) A picture of our heater and the wiring there.

The rep would be unable to issue a replacement unit without this photographic evidence. Each picture had to be emailed, inspected, and then approval had to be obtained from his supervisor before he could issue the RMA. For a thermostat that had an error message on it that was very clearly the Ecobee's failure.

Upon issuance of the RMA, we are to take a picture of the front and back of the unit and send them the Serial Number via email. Nevermind that it's registered in their systems when we purchased it and set it up.

Dearest Ecobee Customer Service Management: If the C wire is checking out in spec, and the Ecobee is saying that it can't tell the temperature (it wasn't -6F in my house this morning) , can't tell the humidity, displays multiple error messages followed by a bee flying around for 10 minutes on the screen, it's ok to let logic rule. My time, and the time of an HVAC professional, are valuable, expensive, and most of all not yours to waste. Your customer service was frustrating. This is not the fault of the poor guy who had to give us redundant instructions; I lay this blame on you squarely and I need you to understand that this was the worst customer service experience I've had in over 5 years. It's memorably bad.

Contrast this with other home automation and thermostat providers I've had experience with and it reminds me that Ecobee has a way to go. This item is in my house running my heat - it's not some ancillary item I can do without in the winter.

TLDR: Ecobee broke in under 90 days, Customer Service had us go through unnecessary remediation (such as changing wires even though we had established the wires were functioning in spec) and then provide excessive documentation before agreeing to possibly send out a replacement unit, but only after we provided more documentation. Meanwhile, I had to hook up a back-up thermostat so I didn't freeze (for those wondering, the back up is working).

Written 27-Nov-2016
I have known for years I wanted an Internet connected thermostat, but working from home made it a "want" not a "need". Purchasing a vacation home made me change my mind and search for the most effective connected thermostat, but not in the way you would think. After much research I decided to buy the Ecobee3. After a month including a one week vacation, I have been DELIGHTED with Ecobee3.

BACKGROUND
My search for an internet connected thermostat started when we bought a vacation home nearly 700 miles away. Just six months early my in-laws moved from 1 mile away to over 300 miles away in another state. My wife & I found ourselves residing several months a year away from our primary home. At roughly the same time my in-laws started returning to visit their friends in the area and accepted our offer to stay at our "vacant" primary home. So I'm hundreds of miles away in our vacation home and my technologically challenged in-laws are staying in our primary home - time for a internet connected thermostat!

I work from home and my office is the "Study" with large windows facing south. The room gets extra warm compared to the rest of the house which otherwise has few southern windows.

In doing my research I had several requirements; 1) security - no amount on convenience is worth insecurity, 2) user interface and ease of programming, 3) integration with automation (something I'll explore in the future), and 4) multiple temperature sensors. This last one is what made me kick myself for not making the purchase much sooner.

SECURITY
While I would have preferred a thermostat that didn't "phone home" for remote access and control, the manufactures has moved that way and I'm reluctantly along for the ride. It was clear I would select a renowned brand and one who developed their product from the ground up with the internet in mind. I've seen problems when manufactures tries to retrofit new technology with older established products.

USER INTERFACE
I was use to the 5-2 systems where you have four daily settings shared by the five weekdays (morning, day, evening & night) and a second set of four settings for the two weekend days. The user interface is button driven and tedious to step through setting it up let alone changing it for vacation. Making matters worst my in-laws would have to set and "unset" the thermostat when they stayed at our home.

From what I read and seen the Nest interface is nice, but I wanted more direct control. Maybe that is possible, but Nest users highlighted simplicity of use over programmability. I had another challenge with Nest - I work from home so it would always register me as home.

AUTOMATION
I am taking baby steps towards home automation. I have Philip Hues lights and August Locks, both of which I highly recommend. I know I will experiment with automation so I wanted the thermostat able to work with Apple HomeKit, Samsung's SmartThings, Wink and other hubs. IFTTT was also a strong desire.

REMOTE SENSORS
WHat I had thought about until starting my research was the ability to manage the temperature by time of day based on remote sensors. I had grown use to manually adjusting the whole house thermostat based on the home office temperature. On sunny days the Home Office gets very warn and I would have to adjust the thermostat. On wintery days the Home Office is colder than the rest of the house. With Ecobee3's remote sensors I'm able to have the daytime temperature sourced from a remote sensor in my Home Office, during the morning and evening sourced from the Ecobee3 itself, and night time from a remote sensor in the bedroom.

This has been transformative in maintaining the comfort level throughout the house. No more ad hoc adjustments made and forgetting to reset to appropriate levels when my work day ends. THIS ALONE MAKES ECOBEE3 THE CHOICE FOR ME.

CLOSING
I've had the Ecobee3 for a month and will continue to monitor the security, reliability, and ease of use. As my experience grows I'll update this review. Same for when I begin experimenting with automation.

** Update 7-Jan-2017 **
I remain extremely pleased with the thermostat especially the Remote Sensors and Vacation scheduling.The sensors have allowed me to achieve a perfect comfort level through the day and over weekdays & weekends. I have made use of remote access in both checking the Vacation mode and invoking the Home mode.
For the holidays I left home for our cottage several days before my family (to get things ready) so I simply pre-programmed the Vacation Mode schedule and it worked perfectly. While we were away my in-laws stopped by unexpectedly and I was able to invoke Home Mode without their involvement.
Our holiday vacation ended a day earlier than planned so about an hour from home i put it in normal mode and arrived to a perfectly warmed home.

I can't remember the last purchase I've made that I have been this satisfied with. Money well spent 10 times over!

For some background, I bought this thermostat to replace the stock Frigidaire thermostat on my furnace. My home has central air an a gas furnace, no heat pump. My old thermostat used two AA batteries for power, and as such, there was no C-wire connected to the terminal on the old thermostat. At first I assumed this would be a showstopper because smart thermostats such as the Ecobee require an external power source. But, as I found out, that is only partially true of the Ecobee - there is a power adapter kit included which uses the existing red wire to power the unit. Lucky for me, I didn't actually have to use the adapter, as there were a handful of extra wires that were run in addition to the wires I had in use. I simply attached one of the extra wires to the C terminal on my furnace control panel and attached the other the C terminal on the Ecobee, and viola, I was in business.

Otherwise, installation was cake. I made sure to turn off all power to my system before starting. Mounting the unit was made extra easy because there's a level built in to the backplate! What a great idea!

After getting it mounted, cabled up, and powered on, the initial setup wizard was a breeze. I was pleased that all of the prompts appeared on-screen on the device and allowed me to punch in my WiFi password and answer a series of basic questions about my home. It proceeded to take about 10 minutes to "calibrate", and then immediately started working.

Before I go any further, there was one minor complaint I had at this point - the packaging. While the packaging itself was fine (the product arrived without any damage, and it was light and sized right), the instruction manual and large round backplate were located on the very bottom - the thermostat itself is on top, then a divider, then under that is the power adapter and mounting hardware. I was completely unaware that there was yet another divider, which concealed a thin round plastic backplate that would have covered the imperfections in the paint job left by removing the old thermostat, and also a few small instruction booklets. Thankfully setup was easy enough that I did not need the instructions.

Had I looked at the instructions, I would have also known not to insert the battery into the secondary sensor before powering on the main thermostat. A quick Google search revealed that inserting the battery upside-down, then reinserting right-side-up would cause the sensor to reset and initiate pairing with the thermostat.

I've only had this thing on for a day, but I'm already blown away by the reporting - and most of the reports aren't even available until it's been in constant service for a month. I'm a numbers junky, and this thing will give me more than enough data.

Most of the preconfigured settings out of the box were fine, but there are so many schedule tweaks, activities, set-points, modes, etc. to explore that I was able to get my thermostat configured exactly how I want it. I'll probably keep playing with it for a few weeks until I really fine tune it, but the level of control and automation is amazing.

All in all, I was skeptical about spending this much money on a thermostat and whether or not it would really meet my needs. I decided to go with this over the Nest because of the secondary sensors and the sheer multitude of options in terms of reporting and configuration, and I am (so far) not disappointed.