"There's an app for that." Who'd have ever thought that would be the case for something as fundamental as a ruler or a measuring tape? But here we are. If you're reading this, you may already know ...

The "Walking Steadiness" feature on iPhone can track how steady you are when walking and notify you if you're unsteady or at risk of falling.

Your iPhone can track steps using a built-in accelerometer. You can track your steps in the Health app, where you can see a range of exercise metrics.