Omron NT31C Reference Manual page 299

Buzzer, Backlight, and Display Control
Caution
!
Reference:
Setting
Operation
288
Do not press the touch panel carelessly while the backlight is off or while the
screen is displaying nothing.
Confirm system safety before pressing the touch panel.
S Even if a position on the touch panel where a touch switch is set is pressed, the
touch switch function is not executed but the screen is displayed.
S If the contents of an element have been changed while the screen is off, the
element is redisplayed in the new state.
No special setting is necessary.
Pressing the touch panel cancels the screen off status to redisplay the screen
which was displayed immediately before the screen was turned off.
Section 3-2