I highly recommend the $200 Resideo Honeywell Home T9 Smart Thermostat. In addition to its straightforward app and optional Alexa and Google Assistant voice controls, the T9 comes with a remote sensor called a Smart Room Sensor. It also has geofencing capabilities that automatically adjust your home and away settings based on your phone's location. 

You can buy the thermostat without the Smart Room Sensor for $170, putting its price in line with models like the $169 Nest Thermostat E, as well as the $169 Ecobee 3 Lite. Google sells a Nest Temperature Sensor for $39, but it only has temperature sensing capabilities. Ecobee's SmartSensors have temperature and proximity detection and are sold in a two-pack for $79.

The Resideo Smart Room Sensor, also sold separately for $40 each, has temperature, humidity and proximity detection. Its comparatively smarter remote sensor, plus its reliable geofencing, set the T9 apart from its similarly priced competition. 

The T9 thermostat is easy to set up, too. Here are the steps, in brief, but be sure to talk to a professional electrician if you have any questions or concerns about your particular HVAC system:

• Turn off power to your thermostat at the circuit breaker
• Remove the faceplate of your current thermostat 
• Take a picture of your current wiring for reference
• Install Resideo's included C-wire adapter (if you don't have a C-wire; I did, so I didn't need the C-wire adapter)
• Remove the rest of your old thermostat
• Feed the wires through the T9's base plate
• Use a level and mark the spots where you need to drill new holes
• Attach the thermostat wires and screw the base plate to the wall
• Connect the T9's faceplate to the baseplate and turn the power back on at the circuit breaker

You should see a light come on, indicating that power is going to the thermostat.

Next comes the app setup. Download the Honeywell Home app and create an account. Select the plus sign to add a new device and then choose "T9 or T10 Pro" from the list of options. The app will then begin to look for your thermostat, ask you to create a home, including assigning it a name and providing your address (this step is necessary for geofencing to work).

The app will ask you various questions about your preferred temperature settings and give you the option to enable geofencing. You can customize the home/away mode geofencing radius in the Honeywell Home app. When you leave the area, your phone will tell the thermostat to switch to away mode; when you return, it will switch to home mode. 

Add your Smart Room Sensor directly on the thermostat. Tap the menu button, then Devices & Sensors. Install the included AAA batteries and follow the steps to name your sensor. You can use your Smart Room Sensor as your default temperature sensor (instead of the thermostat), giving you more control in rooms that tend to run cooler or warmer than the rest of the house. The sensor also has proximity detection, so it knows if you're in the same room and can adjust the temperature automatically for you based on where you are. 

I reached out to Resideo about what location data it collects from the Smart Room Sensors. "We only use the current state (occupied/unoccupied), if the user is making use of the "Active Rooms" feature (which adjusts your thermostat dynamically based on the room you're in). We do not store the sensor occupancy state for analytics purposes," a Resideo spokesperson told me over email. Read Resideo's privacy policy here.

Read more: Best smart thermostats for 2020

Overall, the T9 is a great smart thermostat that's easy to set up and use. I wish it were slightly more affordable -- more like $150 -- but its geofencing, Smart Room Sensor and general performance worked reliably for me throughout my testing. This device can also be added to a broader Honeywell Home security and automation system, making it a great option if you want to scale up your smart home. 

I still like the Ecobee SmartThermostat best as far as high-end smart thermostats go, but the T9 definitely holds its own alongside the Nest E and the Ecobee 3 Lite.