While recording an exercise you can lock both the buttons and screen by keeping the lower right button pressed. Once locked, you cannot change the display views, but you can turn on the backlight with any button press if the backlight is in automatic mode.
To unlock everything, keep the lower right button pressed again.
When you are not recording an exercise, the screen locks and dims after one minute of inactivity. To activate the screen, press any button.
The screen also goes to sleep (blank) after a period of inactivity. Any movement turns the screen on again.