The iPhone is able to detect if you are walking, running, stationary, in a vehicle, or on a bike by using the motion sensors in the device. Back in 2018 I wrote about this in the tutorial called How to Use the CMMotionActivityManager. Today, we’ll update this for SwiftUI.

It is important to note that the information provided by Core Motion has a confidence level. In the screenshot above you can see that I am stationary, but its confidence level is low. Now I was stationary when taking the screenshot, but the movement of the phone probably lowered that confidence level to low.

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In this tutorial we will look at Device Motion which provides various measurements from the sensors on the iPhone. The data is represented by the CMDeviceMotion class which encapsulates measurements taken by the onboard sensors.

Rather than providing raw values from the accelerometer, gyroscope, or magnetometer, the CMDeviceMotion class provides data that has been processed by “Core Motion’s sensor fusion algorithms”. The data is cleaned up, and has bias removed.

In todays tutorial we’re going to look at how to access CMDeviceMotion and create a simple needle that faces down regardless of the direction you rotate the phone around the Z axis. [Read more…]

Updated 20 May 2024

The iPhone packs in a number of sensors. We’ve covered the accelerometer, gyroscope, and magnetometer, and will now take a look at the built in barometer which first appeared in the iPhone 6 and 6 plus smartphones several years ago.

The barometer can be used to detect elevation changes by sensing the changes in air pressure as the phone increases or decreases in altitude.

In todays tutorial we’ll take a look at CMAltimeter which is the class we use to access the barometer.

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New version for iOS 18+ available here.

Using the various sensors on your device, Apple is able to predict if you are walking, running, in a vehicle, or stationary. This is all done quietly in the background by way of the motion coprocessor that is found in all iPhones since the 5s.

In this tutorial we will look at how your app can read that information, either live, or historically from the last 7 days. The CMMotionActivityManager has both the live updates using the startActivityUpdates: method, or the historical data with queryActivityStarting: both of which we will use.

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The Core Motion framework allows your app access to the sensors on the device. The sensors include the accelerometer, gyroscope, and magnetometer. The CMMotionManager class allows access to each of these to get raw data from them so that your app can detect when the device moves. There are a number of applications for this such as sleep tracking, step counting, to name a few. By using a combination of these sensors, your app can calculate information such as your step count.

Creating a step counter could be quite difficult if you were processing raw data and trying to work out the difference between a step and someone just picking up the phone. Thankfully, Apple does the hard work for you by providing you with the CMPedometer class. This class takes this data and provides you with a step count as well as other information such as cadence etc… To make things even better, Apple also provides 7 days worth of history, thanks to the motion coprocessor (introduced in the iPhone 5s). Even if your app isn’t actively running and tracking step counts, the phone is quietly keeping a log of all step counts and statuses and the CMPedometer is the way we retrieve this data. [Read more…]

In this tutorial we will have a look at how to set up the magnetometer using the Core Motion framework. Just like enabling the accelerometer or gyroscope, enabling the magnetometer is also extremely simple to do.

The magnetometer is used to provide measurements of the earths magnetic field relative to the device. You can use the magnetometer to derive the heading, but to do so you would need input from other sensors to help with the calculations. If you are more interested in using the compass, then Apple does cater for that with the CLHeading class which we will look at in another tutorial.

We will begin with a single view application, and work in ViewController.swift. [Read more…]

Yesterday we created a very simple tutorial that let you enable the accelerometer on your device. Today, we’ll look at how to access the gyroscope through the CMMotionManager. These early tutorials are only a very small part of what Core Motion offers, but act as a starting point to show you the very basics of how to get access to the various sensors that Apple has placed in the iPhone.

In later tutorials we’ll look at other aspects of Core Motion and provide some examples of how you might use Core Motion within your own app. [Read more…]

Over the coming weeks we are going to delve in to Core Motion and look at what is available and what can be done with the data that your device provides.

Core Motion was introduced in iOS 4 and provided a way for your app to get data from the sensors on your phone. When Apple introduced the iPhone 5s, they changed the game a little by adding a motion coprocessor. This smaller processor has a single job of handling sensor data recorded by the various sensors on the device even while the device is asleep. It quietly stores this information until the phone wakes up and an app requests the data. The processor requires a lot less power to run, and thus it keeps going 24 hours a day silently keeping this data.

The sensors that Core Motion handles include the accelerometer, gyroscope, pedometer, as well as the magnetometer, and barometer. [Read more…]