If the door lock panel start to flash 'Orange' colour, the battery is low and needs to be replaced.
To replace the batteries, we need following items: A small flat screwdriver 3 x AA batteries
Unscrew the cap of the battery panel with the small flat screwdriver.
Take the battery holder out of the rack. VERY Carefully and quickly take one battery out (let the battery drop) and put in a new battery within 3 seconds. Repeat the previous steps and replace all the batteries.
Put the battery holder back and crew back the metal cap.
Try the panel with a card and see if it is still flashing 'orange'.