Apple issues an update to the software that powers its iPhone, iPad, and iPod Touch devices once a year, and this year's update is finally upon us in the form of iOS 8.

You should routinely update your software and devices for security reasons above all else, but if you're putting off the iOS 8 upgrade, here are a few compelling reasons to download it immediately.

Track Your Health

HealthKit is the name of the API used by developers to collect and manage information about an iPhone user's movement. The technology uses the iPhone's accelerometer, barometer, GPS, Wi-Fi, and (for iPhone 5 and 6 users) connects to the recently announced Apple Watch to monitor the user's heart rate. While the Apple Watch is far from required, you'll find HealthKit is just more useful when supplied with this data.

To access the data, the OS upgrade comes with a new app called Health. Here you can visualize all manner of data and build up a healthcare profile which includes any existing medical conditions, medicines, or allergies. At present, more than 20 health care providers plan to support integration with HealthKit, providing medical professionals with unsurpassed patient data and the possibility of alerts for certain criteria.

HealthKit has been carefully protected by Apple, with stringent privacy policies in place to safeguard the personal data it collects. With iOS 8, your iPhone is your own personal health care monitor.

Send Better Messages

In iOS 8 you can send more than text, photos, and short videos. The new Messages app has support for short, self-destructing voice and video messages. Simply touch and hold the record button with your thumb and record a message, let go and swipe to send it. If someone sends you a voice message, simply lift your iPhone to your ear to hear it.

These messages will all be automatically deleted in time unless you choose to keep them, using the Keep button or by setting Audio Messages Expire to Never under Settings > Messages. It's also easier than ever to share your location -- hit Details then Send My Current Location and Messages will get a GPS fix and inform whoever you're talking to. If you choose Share My Location instead, you can choose to share for one hour, one day or forever.

Also of note is the improved way iOS 8 handles group messages. At long last it's possible to remove contacts (including yourself), mute a conversation using the new Do Not Disturb setting and even give your conversations a name. Message notifications received outside of the Messages app also allow you to reply using a drop-down box, rather than having to launch the app itself.

Make Calls Over Wi-Fi

Whether you're in a rural area, shopping centre, or an environment that simulates the Faraday cage effect, having no cellular reception means you cannot make a call. This was even the case if you were connected to an active Internet connection over Wi-Fi, a frustrating and surmountable predicament. Say hello to Wi-Fi calling in iOS 8.

Your use of this technology depends entirely on whether your carrier wants to support it. At launch, only T-Mobile appears to actually support Wi-Fi calling but AT&T recently announced that support for the technology is coming in 2015. Toggle the feature under Settings > Phone > Wi-Fi Calling, though it presently only works for T-Mobile customers when "T-Mobile Wi-Fi" is displayed in the carrier field. Calls made over Wi-Fi do not count against your data plan.

Type Better & Faster in New Ways

Apple's new QuickType keyboard offers up real-time predictive suggestions while typing. By monitoring your keyboard habits (but not storing this data) QuickType learns which words you're likely to say next. The feature even accounts for style -- using a casual tone in text messages to friends and a more business-like tone with your boss. The feature can even provide predicted answers to questions you are asked by contacts.

If QuickType isn't for you, then iOS 8 comes with user-replaceable keyboards, which you can download from the App Store. Of note is SwiftKey, the keyboard replacement app previously only available on Android that was praised for its customizability and the ability to slide your finger over keys to type. You can sign up on SwiftKey's website to be notified when the iOS app is available.

Share iTunes Purchases & More With Family

After upgrading your family's devices to iOS 8, you can add up to six people as family members, which means six separate Apple IDs linked under one credit card. If you're a parent, you can review requests to purchase apps directly on your own device, as well as view your entire library of purchased apps, music, movies, TV, and books.

Family Sharing has also tied together a few of Apple's older technologies under a familial theme. A new shared family photo album is created on each device you add and a Family calendar helps everyone stay organised. Family Sharing also integrates with Find My Friends and Find My iPhone, allowing you to track family members and lost iDevices should you need to.

iOS 8 Apps Will Be Better

This might seem like an obvious one, but without iOS 8, you won't be able to install iOS 8 apps. This is a big deal because Apple is changing the way apps are able to communicate in iOS 8, so you're likely missing out by continuing to use iOS 7 or earlier. And developers have already had three months to play with Cupertino's big toys, so you can bet some of the larger services will have new ways of interacting with their wares before long.

As an example, custom actions allow developers to tailor their software to a specific task from iOS system menus -- like translating text, applying predefined edits to a photo or saving a selection to a PDF. The ability to share directly to apps is also new, so look out for the ability to open images directly in apps like Instagram or send documents to cloud storage services like Google Drive.

Notification Centre Widgets

While Android users have had widgets for years, these have traditionally lived on users' home screens. That was never likely to happen on iOS, and so Apple has instead settled on the more predictable Notification Centre as a location for third party widgets. In iOS 8, these widgets are extensions of third-party apps which can display information about the weather, your data plan, or the latest football scores.

The Camera is Better

Yes, the iPhone 6 and 6 Plus both offer compelling reasons keen smartphone photographers might want to upgrade, but iOS 8 itself includes enhancements that will improve the results you get from your current hardware. The ability to control focus and exposure separately has been long coming; simply tap an area to focus then slide a finger up and down the focus box to adjust exposure.

There is a new mode for taking time-lapse video which shoots multiple still images at a set interval, and while offering little control, it does make the whole process super simple: hit record and let your device deal with the rest.

A self timer has been added to the standard camera mode, for better group shots and more dramatic selfies. Finally, the iPad gets Panorama mode, and there's improved support for burst mode on older devices -- previously only found on the iPhone 5S in iOS 7.

The Photos App is Better

Apple is touting its redesigned Photos app as one of the best iOS 8 features, and if you're a photographer there are a few reasons to smile. iCloud Photo Library replaces Photo Stream, which maintains organisational structure across your devices whether it's an iPhone, iPad, Mac or other PC via the web. Smaller devices get a break with cloud storage taking over, and smart caching and offline storage of images makes the most of your available space.

There are also improvements to the way photos are organised. Add a photo to your favourites and it will appear in the favourites album, which is synced across your devices. A new search and smarter filters make it easy to find things among the huge volume you're sure to amass. Far more advanced editing tools make an appearance, complete with support for third-party filters from app developers.

Naturally storing all of your pictures in the cloud (or iCloud to be specific) is going to cost you. Apple lowered their iCloud pricing in June but still won't offer any more than the measly 5 gigabytes we're used to for free. You can get 20 gigabytes for $12 per year or 200 gigabytes for $48 per year. More storage will become available for those of you who need it, especially when the new Photos app for Mavericks launches.

Spotlight & Siri Do More

Last of all come two features (that people don't often use until they realise quite how useful they can be) that have just gotten a little more useful. Spotlight has received a flurry of new sources to search including the App Store (at last!), Wikipedia, news events, nearby locations, and movie times.

If your iPhone is plugged in, a "Hey Siri" will tell it to listen up for a command -- just like Android's "OK Google" feature. When you speak, Siri will update you with what it thought you said in realtime. And if you don't know what music is playing around you, just Siri it -- it's connected to Shazam.

How To Get It

iOS 8 is compatible with the following devices:

  • iPhone 4s, 5, 5c, 5s, 6, 6 Plus
  • iPad 2, 3, 4, Air, mini, mini with Retina
  • iPod Touch 5

To download, visit Settings > General > Software Update on your device while connected to a Wi-Fi network to download, verify, and install the update. You should create a backup of your iOS device before installing any major updates, just in case something goes wrong. You can also connect your device to a Mac or computer with the latest version of iTunes and click the Update button on your device's Summary tab.

Note: It is advised you refuse upgrading to iCloud Drive until OS X 10.10 Yosemite is released if you rely on shared iCloud data between OS X and iOS. If the update doesn't show up straight away, wait a while -- lots of people will be downloading over the next few days.

Still To Come

As mentioned, iCloud Drive and the other Continuity features are yet to be seen. At present, we're still waiting for Apple to announce an OS X Yosemite release date -- the free upgrade ties in with many iOS 8 features, and there's even an OS X equivalent to the new Photos app arriving in the new year.

Have you upgraded to iOS 8? What do you like about it? What don't you like?