Turning On and Off Talkback and Voiceover with Home Key

For Talkback on Android

1. Go to App, select Settings.
2. Swipe 1-finger right for Accessibility.
3. Open Accessibility, swipe right and select Direct Access.
4. If you hear Talk Back read Direct Access Off, Double-tap to turn   it on.
5. Direct Access will list some applications that enable to shut down and open by pressing the Home key three times quickly. In the list, swipe 1-finger right or left to find Talk Back.
6. Double-tap to select this item.

Now, you can turn Talkback off while being off by pressing Home key three times quickly and in reverse.

For Voiceover on iOS

From the home screen, follow steps below:

1. Find and open the Settings Button.
2. Swipe 1-finger right for General Button.
3. Open the General Button and then continue swipe right to select the Accessibility Button.
4. From Accessibility Button, swipe right and find the last item called Accessibility Shortcut.
5. At this point, VoiceOver will tell you which application is currently selected to turn off and on when pressing the Home key three times quickly. Under the Triple-Click the Home Button For item, just like on Android, iOS lists some applications that allow you to turn off and on with Home key. Choose Voiceover as the app for this option.