How To Take A Screenshot or Screen Capture With The Sony Ericsson Xperia Arc:
Unfortunately, the Sony Ericsson Xperia Arc cannot natively take screenshots 
However, users can root the device or install the Android SDK to take screenshots. There are many guides out there to achieve this, but be careful!
How To Take A Screenshot or Screen Capture With The Lenovo K3 Note To take a screenshot or screen capture with the Lenovo K3 Note Press and hold the VOLUME DOWN and POWER buttons at the same time....
How To Take a Screenshot or Screen Capture with the Nokia XL To take a screenshot or screen capture with the Nokia XL, simply: Hold down the VOLUME DOWN button and the POWER button...
How To Take A Screenshot or Screen Capture With The OnePlus One To take a screenshot or screen capture with the OnePlus One: Hold down the POWER button and the VOLUME DOWN button at the same time....
How To Take A Screenshot With Nexus 4 To take a screenshot or screen capture with the Nexus 4: Hold down the POWER button and the VOLUME DOWN button at the same time....