LG E440 Quick Reference Manual page 291

NOTE: Proximity sensor
When receiving and making calls, the
proximity sensor automatically turns the
backlight off and locks the touch screen by
sensing when the phone is near your ear.
This extends battery life and prevents you
from unintentionally activating the touch
screen during calls.
WARNING
Placing a heavy object on the phone or
sitting on it can damage the LCD and
touch screen functions. Do not cover
the LCD proximity sensor with protective
film. This could cause the sensor to
malfunction.
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