You can tweak so many things in Android, you probably haven't even bothered opening up the Accessibility settings. Given the name, you'd think those are only features for people with disabilities, but they can actually be useful for anyone.
Zoom Anywhere with Magnification Gestures
Enable "Magnification Gestures" and Android will zoom in on anything you want (except the keyboard and notifications bar), whether the app allows for it or now. It's easy to implement too. Just triple-tap any part that you want to magnify, and then pan with multiple fingers. Pinching adjusts the zoom level.
There's also a shortcut if you use this feature often, as Google puts it in the app itself:
You can also temporarily magnify what's under your finger by triple tapping and holding. In this magnified state, you can drag your finger to explore different parts of the screen. Lift your finger to return to your previous state.
You can zoom in on your favourite Instagram images with this little trick, for example, since Instagram doesn't allow for regular pinch-to-zoom. And, of course, any other app too.
Hang Up with the Power Button
When your phone rings and you need to quickly cut the call, press the Power button -- that's all you'll have to do if you enable "Power button ends call" in your Accessibility settings.
There's nothing more to this one, but the option itself is useful. It's the setting I first enable in any Android phone because I often have my phone in my pocket. If you're in a meeting or busy in any way, you can just cut the call and have it go to voicemail, without ever taking your phone out of the pocket. Plus, it is also useful if your proximity sensor takes a few seconds to register the tap to end a call after talking.
Turn Any Book into an Audiobook
Google's built-in "Text-to-speech output" option can turn any ebook into an audiobook, says CNET. It won't work with Pocket or even Kindle, but with the Google Play Books app, you can have any book read aloud. The best part? You can customise the voice to how you like it.
Because it's Google's own engine, you can choose from the various voice data options for an accent or language that best suits your preferences. For example, with English, you get options for United States, United Kingdom or India. With Spanish, you can choose between the US or Spain. You can also set the rate of speech, choosing between nine speeds. Tap the "Listen to an example" to get it just how you want it.
Once Text-to-speech output is set up, go to Google Play Books and open your ebook. If you didn't buy it from the Google Play Store, don't worry, you can easily import all your ebooks into Google Play Books. In the app, go to Menu > Settings and enable "Automatically read aloud" to have Google read any book you open.
CNET recommends that you also enable another option:
You'll also want to ensure that "High-quality voice" is turned on as well, otherwise the speech sounds a little too robotic.
Be warned that the "High-quality voice" setting requires you to use data, so only enable it if internet charges or speed aren't a concern.
Get Larger Text System-Wide
If the font size of your device is not big enough -- and it often isn't, especially if you need reading glasses -- then Accessibility settings can provide relief. There is an option here to enable "Large text" and it works across the system. So your font is made larger everywhere, thus making it more legible too.
Enable and Disable Accessibility Features with a Shortcut
While you have all these Accessibility features, you might not want or need to use them all the time. A simple shortcut lets you enable/disable them quickly.
Take, for instance, the Large Text option. You might not want that bigger font all the time, but you can keep it enabled and only switch it on and off as required with this shortcut. Now, the Accessibility shortcut can be activated in two ways: by pressing and holding the power button or by touching and holding two fingers.
Pressing and holding the Power button was a no-go for me, and would be for many people, as it brings up the shutdown menu for Android. When you're touching and holding two fingers, make sure it's on a place where you can't trigger some other action -- for example, doing it on the homescreen will probably bring up widget and launcher options.
These accessibility options should help you get more out of your Android without installing anything. There are other options too, such as Talkback, but those are made for certain disabilities in a way that they require you to change how you normally use Android.