The battery pack is inside the door and batteries can only be replaced with the safe open. To access the override lock, there is usually a removable panel to the side of the keypad. Undoing this will uncover the lock for the key to be inserted. If you have lost the override key then you cannot open the safe.
Safe with an emergency power supply: without battery power, you can't physically open this type of safe. To give your keypad enough power to be able to input your code, hold up a 9V battery (such as the ones you find in smoke detectors) to its connection points.
Insert a knife into the keyhole and shake it to pop the lock open. If your digital safe has a keyhole, stick the pointed tip of a sturdy knife into it. Shake and wiggle the knife to force the locking mechanism to disengage. Then, open the door of the safe.
Jammed bolt work
The jam can be the main reason your safe won't open as you hear the motor trying to retract the bolt work. Here's what you can do: press firmly on the door a few times to loosen the bolt work. But make sure not to press on the keypad and handle.
With a scope, a locksmith will drill a small hole into the side of the safe. Then, through the hole, the locksmith will insert a small scope. With the scope, the locksmith will be able to see how the lock works, from the inside. The locksmith will then be able to deactivate the lock from the inside.
This means your combination code is retained even if the battery has gone dead and is no longer powering the lock. If this happens, simply replace the battery. For added security, you can deliberately remove the batteries from the lock and replace them when you need access to the safe.
The most direct method is to drill into the face of the lock in order to reach the lever or drive cam. After accessing the lever or cam, the safecracker can use a punch rod to push them out of the way or bend them until they are no longer obstructing the path of the bolt.