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

1.0 out of 5
2 Ratings

2 Ratings

Simba IV ,

Don’t buy

I bought the app yesterday (sep 03, 2019) but the app doesn’t work at all. First, it asks you to enter the current temperature for it to ‘caliberate’. But then why would I need a thermometer, if I knew the temperature in the first place. Second, the temperature it ends up showing is highly dependent on the input temperature. Third, the way it says it would work is also strange and inconvenient. In general, it was a big mistake for me to purchase it. Don’t buy it is scam.

Developer Response ,

Hi Simba IV,
Sorry to hear that you had problems getting the app to work for you. The way that the app works is by sending a sound out of the earpiece of your headset and measuring how long it takes for the sound to reach the microphone (an acoustic thermometer). This when you first set up the earpiece and speaker, the app needs to calibrate to the current temperature as the distance you set up is unknown. This is why the app asks for the temperature when you first calibrate - you can then use your set up to measure different temperatures e.g. inside v outside, different rooms, etc.
Yes, the temperature displayed is dependent upon the temperature - that is what the app is designed to do (?).
Agreed, at the moment, using the headset is not a very convenient way to measure temperature which is why it is still described as an experimental application. As far as we are aware this is the first application in the world on a smart phone that is measuring the speed of sound to sense temperature. We are trying hard to improve this app so that it will work with the onboard speaker and microphone, which would make it much more convenient and robust.
It is not a "scam". We have been working on this application for many years to get to this stage and when set up correctly, it does measure temperature in a very responsive and accurate way. I am sorry if you feel you have been misled and wasted your money. This is certainly not our intention. Please request a refund from the App store and you should get your money back. Thanks for your interest in Ondo.

Lovely Lisa 23 ,


Downloaded this App to find out the temperature. It makes you jump tho hoops to set up and then asks you to enter the temperature to calibrate the App. I wouldn’t need the App if I KNEW the temperature!! How stupid!!!


SCB Associates Ltd
27.6 MB

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



Age Rating


  • Family Sharing

    Up to six family members will be able to use this app with Family Sharing enabled.

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