Smart thermostats are essential to building out your smart home, but they have two things going against them: price and compatibility. Neither is an issue with the Emerson Sensi Wi-Fi Thermostat, which you can for just $89 with a special promo code.

The Sensi normally sells for $129 on Newegg, and that’s its typical retail price. However typing in the promo code NEWEGGSENSI40 brings the price down to $89, far cheaper than we’ve seen anywhere else. We’d recommend you act soon as it appears the code might expire as soon as tonight at midnight Pacific Time.

Also, if you’re lucky enough to have a utility provider that offers rebates for the purchase of any smart thermostat, you may be able to effectively get this even cheaper. Some providers offer as much as $50 back, so be sure to check.

Our experience with the Sensi wasn’t one that knocked our socks off, but it did handle the basics of smart control of our HVAC system well. Where it sets itself apart is its battery operated nature: using only 2 ‘AA’ batteries, this thermostat is compatible with older HVAC systems, often referred to as ‘millivolt’ systems.

If your heating system has one of those old-school circular-dial Honeywells, or uses radiators, chances are it’s a millivolt. No power is provided to the thermostat itself, which rules out a Nest, ecobee, or most other smart thermostats.

It’s not cheap to run power to your thermostat either: I’ve gotten estimates in the thousands because of the rewiring necessary. It’s just not worth it. But even those with non-millivolt HVAC systems might want to consider this thermostat for the price alone: it does the basics well.

You’ll get 7-day programming, a monochrome screen that has a backlight that turns red when heating and blue when cooling, Alexa, Google Assistant, and IFTTT support, and a decent app. Is it a Nest? No, but it’s not trying to be.

But we do understand that for some, the Sensi might be a little too barebones. For these people, we’d suggest the Honeywell T5+, which while still utilitarian does a lot more and is closer in feature set to the higher-end smart thermostats. Best Buy currently has the T5+ on sale for $100

With the Honeywell T5+, you’ll gain geofencing capabilities which allow your thermostat to detect your presence, and the capability to learn your heating and cooling preferences over time. But you’ll need to have a power line running to your old thermostat, as millivolt systems aren’t compatible.

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