Measure indoor room temperature using your iPhone or iPad and headset (required).

Ondo® is an experimental acoustic thermometer implemented using an iPhone (or iPad) and headset. Acoustic thermometers utilise the principle that the speed of sound in air changes with temperature; by measuring the speed of sound it is possible to calculate air temperature.

How it works?
Ondo® transmits a high frequency sound from the headset earpiece. This sound is received by the microphone positioned a short, fixed distance from the earpiece. The time taken for the sound to travel between the earpiece and the microphone is very accurately measured to less than a millionth of a second.

What you will need to build your acoustic thermometer:
• Standard Apple headset (EarPods with lightning connector)
• Old credit or debit card (to provide a base)
• Four elastic bands (to hold the right earpiece and microphone in position)
• iPhone or iPad with Ondo® installed

Getting started:
• Follow the simple instructions in the app (or on the website to build your headset thermometer
• Calibrate to the starting temperature and your thermometer is ready to use
• Move the phone and headset to a different temperature zone e.g. take it outside or move nearer to a heater and watch the reading change

• Temperature range -40 to 50 degrees Celsius
• Accuracy +/- 1 degree (dependent upon headset fixing)

PLEASE NOTE - This app will only work with a headset connected and set up according to the instructions in the app. Please do not buy this app if you do not have a suitable headset. This app will not work with AirPods.

What’s New

Version 1.1

Improved calibration and temperature reading stability.

Ratings and Reviews

1.8 out of 5
5 Ratings

5 Ratings

Mike2567 ,


App is buggy ... doesn’t always see the headset and has to be restarted periodically. And the readings are inaccurate. I mean way off like 15 degrees. Great concept but right now it’s a toy. Maybe an updated version will be better.

Developer Response ,

Hi Mike2567,
We really appreciate your very constructive feedback. We are still working hard on trying to improve Ondo. We will look into the problem with the headset recognition that you have experienced.
I am surprised to hear about the accuracy problem that you have found. In our very extensive testing we have found that it should be accurate to within one or two degrees. It does require that the positioning of the earpiece and the microphone is very stable - even a tiny movement will cause quite a big temperature change.
We are currently working on a version that will utilise the iPhone onboard speaker and microphone which will hopefully be more robust and considerably more convenient!
Thanks again for taking the trouble to let us know your experience.
Best regards,

stoneallen ,

Does not work!!

Did not work, got no calibration screen after I set it up like instructions. But they still got my money is what pisses me off.

Developer Response ,

Hi Stoneallen,
Very disappointed to hear that you have had problems getting Ondo to work. If you have followed the set up screens then the calibration button should be available on the last screen (Note- you may need to scroll down to find it). Alternatively, once the app is installed, you can re-run the calibration from the options menu.
If this does not work and you are still not happy, then please request a refund directly from the app store. We do not want to take your money if you are not completely happy and certainly do not want to upset you.

girl2no ,

Rip off

I have an iPhone!! No headset. What a waste! This need to. E taken off the iPhone App Store!!


SCB Associates Ltd
27.6 MB

Requires iOS 10.0 or later. Compatible with iPhone, iPad, and iPod touch.



Age Rating


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

You May Also Like