The app worked fine until yesterday. Now it keeps crashing. Reinstalling does not help.

This is an iOS bug. Please try to soft reset your phone following the instructions on this page.

The app keeps closing when I tap "START".

It's essential for Pulse Oximeter to have access to the Camera. Please go to the iOS Settings App, scroll down and find "Oximeter", and allow Oximeter to access the Camera.

Pulse Oximeter doesn't show up with Apple's Health App in Sources.

After the first successful measurement you'll get a pop-up which asks for permission to write to Health. Turn on sharing for both heart rate and oxygen saturation and you're good to go!

The app doesn't work with iPhone 6/6+

The slim design of the iPhones 6/6+ results in a protruding camera lens. When placing your finger on the camera and the flash, make sure to only touch—not press—your finger on the camera and flash. If the protruding camera makes an indention on your finger, the app won’t work properly.

I consistently get low SpO2 levels.

You might be pressing too lightly/hard down on the camera lens or your phone might be running hot (an issue with the iPhone 4S). Make sure to wait for the calibration to finish. If you keep getting "--" warnings, remove your finger, tap "Stop", then "Start", and replace your finger on the flash and camera lens after ½-1 second. Also, the app doesn't measure values below 93%.

Tapping "Results" or "Start" makes the app crash.

Press the "Home"-button to exit the app. Long-press the app icon, then tap the "X" to remove the app. Reinstall it from the App Store. This will erase all your data, so export first for safe keeping.

My readings are very irregular/off the charts. Am I holding it wrong?

Be sure to hold the phone as shown in the App Instructions. Alternatively, try to restart the app.

I have trouble getting correct measurements after working out or if I feel stressed.

The app can be susceptible to tremors or other movements. Try sitting and resting your hand against a table or some other solid structure.

I get lower SpO2 levels when measuring in darkness.

If it is completely dark, camera-calibration will be slightly off. Even a single, minor light source in the room will result in better results. You might need to exit and re-enter the app for the calibration to reset though.

How hard should I squeeze the flash?

From update 1.3.2 and forward you no longer need to squeeze. Just cover the flash and camera lens evenly with your finger.

Can I use the app during training?

If you manage to get steady results while resting it is actually possible to get steady results during exercise as well. Try it out and let us know what you think.

Can I use the app if I have an iPhone case?

We recommend that you remove the case as some cases interfere with the accuracy of the app.

What should I do if the progress bar lags or the data curve produces less noise or a smaller Heart Rate spike?

You can try to fidget your finger a little around, apply more or less pressure or exit the app and try again. The data curve will change to show a better/worse signal as you do this.