LG Nexus 4 Quick Start Manual page 12

When Nexus 4 is on, press the Power button again to
put it into sleep mode or wake it up.
to turn off your Nexus , press and hold the Power
button until a confirmation dialog appears. Then touch
oK to complete the shut down.
to restart your Nexus 4 if it becomes unresponsive,
press and hold the Power/Lock key for at least 10
seconds.
tIp: to quickly silence your phone or toggle
airplane mode, press and hold the power
button for one or two seconds to see a quick
confirmation dialog – even from the lock screen.
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