DoorCam generally runs up to twelve months on the original 3 D batteries included. Some factors that might contribute to the batteries running out faster include high foot traffic at DoorCam's entryway or having the Live View Option on for an extended amount of time.
If your batteries are running low, keep calm! DO NOT hit the reset button. You can purchase more D batteries from the closest store that sells them. Once you have them, just pop off the back of your DoorCam, take out the old batteries, put in the new batteries, put the back on again, and you're ready to go! No need to remove DoorCam at all from its surveillance position.