electric meter and voting machine have seals on, broken seal means tamper. You can get tape that says void for that., best way depending on what your trying to protect is to try and encrypt the data, but NOTHING is unhackable. People have even used nitric acid to decap a chip and read the silicon wafer.
If the info is that valuable then put a explosive inside the box and get it to trigger on opening the case, a few more hand less thieving B'stards in the world would be a good thing.