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iPhone and Android Control

The Heat Guardian does not currently have software for iPhone and the Android software is in early Beta test. There is a solution that works well but is a little clumsy until iPhone/Android get completed.

The Google Play Store and the iPhone App store both have an application named "Nrf Toolbox" designed for Bluetooth. This app works very well with the Heat Guardian. Here is how to use the Toolbox to set minimum and maximum temperatures and to monitor the units via Bluetooth.

Android: this application must have Location permission (on Android). That makes no real sense but... Android. Select "Always" location permission and make sure your phone settings enable Location or the application will not work.

You may pair the Heat Guardians to your phone Bluetooth. That makes clicking a little easier.

Install Nrf Toolbox

Start by installing Nrf Toolbox from the Play Store (Android) or App Store (iPhone). When you run the program it shows the various subprograms within it.


Heat Guardian supports exactly 3 of these subprograms, the

  • DFU (device firmware updater

  • HTM (health thermometer)

  • UART (command line interpreter)

In order to set the temperature range, run the UART application.

Click the UART icon to start the subprogram and begin.

Connect to the Heat Guardian Command Line

After starting up the UART application, click the CONNECT Button.


This lists all nearby Bluetooth devices. The Heat Guardians are named HeatGuardian.RX and HeatGuardian.TX. If you look at the labels on the back of each Heat Guardian you'll notice one says type: R and one says type: T. That's RX and TX.

Pick one of the HeatGuardians. You can make this change to both units or just to the unit you'll keep with you.


Set Temperature Range


We will send the following commands to the Heat Guardian:

  • cz4 -> Play the find me tune on the Heat Guardian to verify that it is connected.

  • cr4 -> Retrieve the min/max temperature range to see the current settings

  • ct110 -> Set the upper temperature to 110°F (you may use any temperature)

  • cu55 -> Set the lower temperature to 55°F (you may use any temperature)

  • cr4 -> Retrieve (again) the min/max temperature range to verify your changes


Start by swiping the screen right. On the iPhone drag the UART left border to the right.

The grid will be replaced by an entry screen. See below.


Click the "Write command" line at the bottom (the iPhone line is at the top and seems to wrongly say "No UART connected") and type cz4 then click SEND. The Heat Guardian should play a tune.


Now click the "Write command" line and type cr4 and click SEND. The Heat Guardian will return information showing Max, Min temperatures (and power). See the next images->


In the above Android image on the left, you can see that the response was _M130_m40_P17. The iPhone image is of a different unit.

So, the max temperature is now 130°F and the min temperature is 40°F (and the power is 17).

To set the max to 110°F and the min to 55°F and re-verify,

    using the Write command line and SEND button as above...

  • send ct110

  • send cu55

  • and send cr4.

See below.



The result from the last cr4 does show the correct settings.

When you are finished, swipe left to return to the UART screen and click the DISCONNECT button.

Monitor the Heat Guardian

If you would like to use your phone to monitor temperature, the HTM (health thermometer) application works with Heat Guardian. When it connects to a Heat Guardian the temperature and battery shown are for the Remote unit.

Start HTM from within the Nrf Toolbox and connect to the local Heat Guardian. The temperature and battery will update every 30 seconds.

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