A Smart Thermostat with Geofencing for Under $100

Where We Started

We replaced our non-programmable thermostat some time ago with a Nest thermostat. Besides it’s beautiful aesthetics, we were primarily interested in lowering our heating and cooling utility bills.

Shortly after purchasing the Nest, we realized that the Nest way of reducing our HVAC usage didn’t make sense for our house occupancy patterns. We determined that we needed to control the Nest in a different manner to really make it save money.


Adding Geofencing to the Nest Learning Thermostat

I have what I call an anti-schedule. I don’t head to work and return home at the same times each day of the week. I may work at home until 11:00 AM before heading to the office, or may be home rather late if I have an engagement in the evening. Weekends are even less predictable. I may take off to the coast at an early hour to get a day of surfing in, or, I may sleep in, have a friend over for breakfast and coffee, and enjoy time at home.

The Nest Learning Thermostat is designed to learn your patterns without you having to teach it. How can the Nest learn your schedule when you don’t have one? You quickly end up needing to manually program in a schedule to the Nest which sort of works, but is wrong a good deal of the time.

Nest, in the product’s defense, tries to solve this problem with a feature called Auto-Away. It keeps track of activity near it with a motion sensor. If it doesn’t see motion for a span of time, it assumes you’ve left and sets itself to away, overriding the schedule. If it sees motion again, it sets itself back to home. The amount of time it takes to do this spans somewhere between 15-120 minutes, depending upon learned behavior, according to Nest.

The problem with Auto-Away is that it gets it wrong a good deal of the time. If I’m working from home in my office, Nest will think the house is empty. If I actually do leave the house, the Nest sometimes takes longer to realize I’m gone than I’m actually gone for.

This lead to the question: how can I passively keep the Nest updated on my location at all times? Other thermostat manufacturers achieve this with a technology called geofencing. Geofencing is a way of creating a virtual perimeter around a particular space. When you cross this line, some sort of event occurs. The answer for us was to build an app that could keep track of whether we were within a geofence around our home or not, and update Nest accordingly.

Out of this, we created Skylark, a mobile app that keeps track of whether anyone is home or not and updates your Nest when your home empties out and whenever someone comes home.


Unexpected Realizations

The first month of using Skylark in beta was great. We found that our Nest home/away setting changed instantly whenever we arrived home or left. Finally, our Nest status was based on our actual location, not on what the Nest guessed was our location.

We had a problem though. Sometimes our Nest would still set to away while we were home. Other times, it set to home even though we were gone. Auto-away was still wreaking havoc on the Nest status. We realized that we didn’t need it any longer, as Skylark did a better job of determining our status than it ever could. We disabled it.

With Auto-Away and the schedule learning feature disabled, our Nest was turning more and more into a normal thermostat. This got us to thinking: if we hadn’t already owned a Nest, what would we purchase now? Is it worth paying the Nest premium if we aren’t using most of the features?


Commodity Hardware Options?

We considered building our own thermostat. What would it need to have? A basic thermostat with a schedule would suffice. The only extra feature we’d need is WiFi. From there, we could use Skylark to add the magic. But how would we produce at a large enough volume to justify selling a hardware product like this? How would we compete with a company like Honeywell?

A routine visit to Home Depot turned this question on its head. Honeywell already makes a variety of WiFi enabled thermostats. Could we potentially integrate with one of them, adding the much desired geolocation feature to an otherwise unremarkable thermostat? Yes we could.


The sub $100 Smart Thermostat

After some additional engineering effort, we were able to add Honeywell thermostat support to Skylark. Using almost any Honeywell WiFi thermostat, such as this one ($92 at the time of writing this article), we had a geofenced thermostat solution that is every bit as good at saving energy costs as our Nest thermostat is.

Are the Honeywell WiFi thermostats as aesthetically sexy as the Nest thermostat? Not really. Does it save on energy costs just as effectively at less than half of the price of the Nest? Absolutely, and we think that’s pretty sexy, too.

Skylark for Nest & Honeywell Smart Thermostats is available in the Apple App Store.
Most Honeywell WiFi enabled thermostats should work with Skylark.