First Alert created and launched their first ever home product, a commercial smoke alarm in 1958.  Since then, they have produced different home safety units and have made a name as America’s one of the most trusted and reliable brands. 

In the October of 2015, ventured as a smart Thermostat producer that can be integrated into digitally interconnected homes. 

First Alert One Link

Therm 500 Onelink offers all the basic amenities like W-Fi connectivity, temperature control through Onelink app and sophisticated programmable modes that adjust the temperatures to maximize comfort and efficiency. 

There is much more to this little smart wonder from FirstAlert, which we shall discuss here in detail. 

Quick Highlights of the FirstAlert Onelink Thermostat

  • Customizable Wallpapers – This is one of the unique features of this thermostat, you can add up to 100s of wallpapers into your thermostat display. This gives the thermostat a more personalized attire. You can even edit the wallpapers displayed in the thermostat background.
  • Custom Schedules – You can schedule the onelink thermostat with pre-defined settings. You can program the thermostat in different time intervals(morning, noon, evening, night etc).
  • Security – You can lock the thermostat with screen lock password so that no other persons(or an outsider) can change the temperature unwantedly.
  • Reporting – FirstAlert Onelink thermostat has excellent analytics through which you can how the thermostat functions and saves energy.
  • Easy installation – The onelink thermostat can be installed very easily in 20-30 minutes. The company also gives you technical phone support for installation.

The colourful touch screen Display

Therm 500 Onelink from first alert is sized at 1.2 x 5.2 x 4 inches and weighs around 1.55 pounds. One of the striking features of this Thermostat is its beautiful, colourful display. The font sizes are readable, icons pretty easy to understand and the menu easy to navigate. You can read the display even if you are several feet away across the hall. The touch-screen works very well, provided you press at the right spot. 

All the important information about the room temperature, current time, working mode of the HVAC system etc can be learnt via a glance at the screen. There are up/down touch buttons on the screen to set or change the temperature. 

The screen brightens up when it is touched for changing or viewing the settings, the brightness of which can be set according to your convenience. You can dim or bright up the screen at any time. This makes it easily readable at any time of the day without being harsh on the eyes. 

You can set wallpapers and screen savers too; either choose from the already in built wallpapers or set custom wallpaper. You will need to download the app for uploading the custom wallpaper from the SD memory card. The screen saver gives a digital photo frame feel to the screen when the Thermostat is sitting idle. 

The touchscreen can be locked via the automatic screen lock option. This prevents wandering hands from accidently resetting the whole system. The fan icon shows two options once it is pressed: the auto and the on mode. When the fan is in “ON” mode, the fan will continue to run even in OFF mode, while in “Auto” mode, the fan works only when there is a cooling or heating demand. 

The Thermostat comes with an inbuilt humidity sensor, which senses the humidity of the room and displays the value on the screen. You can then use the dehumidifier of your AC to dehumidify the room. The Thermostat, however, keeps a control on the temperature so that the room is not cooled over the set temperature.  

The Onelink App

The android/iOS app for the Therm 500 Onelink Thermostat has been designed to be very user friendly. Once you download the app on your device and connect it to the Thermostat via Wi-Fi, you will be bombarded with all the necessary information. You can keep monitoring your energy usage and choose a program that will give you the most efficient results.  This helps in reducing the energy costs, and saves energy from being wasted. 

You can create a 7 day schedule with 4 periods for each day. The app also lets you control the schedule from any part of the world. You can be returning from office and setting a temperature to make your room cosy, or you could be turning OFF the Heating system after you’ve forgot to switch OFF before leaving the house. 

You can also send messages to the thermostat from your app, personalize and give names to your Therm 500 Onelink Thermostats placed at different rooms of your home (to distinguish between them). 

The trigger Home/away feature lets your thermostat know before hand the timings or day when you are out or at home. This helps in maximizing your comfort. 

Apart from viewing the indoor temperature and humidity, the app also lets you view the outdoor temperature and humidity level. It also sends weather forecast for the next 2-3 days, to help in scheduling your programs for the coming days. 

Amozon Alexa on your command!

Love Alexa? You will be glad to know that all you need to do to change your temperature settings is just ask Alexa. The Therm 500 Onelink Thermostat is compatible with amazon Alexa. With simple commands like “Alexa set the temperature to 64 degrees Fahrenheit/ Lexa incease the temperature by 5 degree Farenheit / Alexa cool the room”, the indoor room temperature can be set without going through the pain of taking out the mobile app or going physically to the Thermostat to make the change. Howevr, if you just say “Alexa, cool/heat up the room”, then it will decrease or ncrease the exisiting temperature by 2 degrees by default. 

Safety comes first!

Following their age old tradition to keep your homes safe, first alert Therm 500 Onelink Thermostat sends E-mail alerts to its users, whenever the indoor temperature exceed or drops below the preset temperature therholds. This avoids unnecessary damage of your HVAC systems.   

Quick and Easy Installation

The Onelink Therm 500 unit comes with an illustrated installation manual that guides you to get through the installation process. Check if you have 5 wire connection, if yes then installation will be a piece of cake for you, provided you are an experienced technician. We always strongly recommend that you take  a professional help for installation of the Thermostat, if you aren’t familiar with house wirings. 

Timely maintenance reminder

One thing we often forget or overlook is the proper maintenance of our HVAC system. With FirstAlert’s Therm 500 Onelink Thermostat you need not worry about missing out in cleaning the air filters. The Thermostat sends you a reminder every time it senses a need to change the air filter or a need for overall maintenance.  

Link multiple Therm 500 Onelink Thermostats via cloud

If you have multiple heating/cooling zones at your home, then you can use separate Thermostats for the different zones. In order to control multiple Thermostats, connect them together via cloud so that all of the Thermostats will show up on your Onelink app. You can then control them independently. 

Auxiliary heat lock out function

The Thermostat has another distinctive feature where the heat pump ramps the heat up such that the auxiliary heating system does not need to be started, unless it gets very cold.  The auxiliary heat lockout feature lets you choose a temperature below which the Thermostat will not start the auxiliary heating system. 

Power Source

The Therm 500 is a low voltage Thermostat and hence works with 24 volt direct power supply. There is no battery backup. Therefore, in case of power failure, it will go off. Once the power is restored, it will reboot to its previous settings. There is a SD card slot, which can be used as back up for replication of the settings and security.  

This was a general brief review of the Therm 500 Onelink Thermostat from the house of first alert. Before we wrap up the article, below are some of the important pros and cons of the product. 


  • Rich, colourful touchscreen display with customized wallpapers and screensavers
  • 7 day  (4 periods per day) programming and remote controlling of indoor temperature through the Onelink app
  • Responsive and backlit touchscreen display
  • Alert for air filter change and maintenance 
  • Auxiliary heat system can be locked out for a certain degree of temperature
  • Easy to use and understand user interface
  • Lock screen option to prevent wandering hands from resting the program
  • Gives a 2-3 heads up through a weather forecast which helps schedule a program better. 
  • Listens to Amazon Alexa


  • Not compatible with other voice assistants like Ok Google or Siri. 
  • No battery back up
  • The process of changing the wallpaper and screen saver is complex

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