It is a fact that no safe can ever be impregnable. Even a meter thick titanium box could be cut through eventually. Security measures are designed with the intent of making any attempted break in so time consuming and recognizable that the thieves will be apprehended before they can succeed. So long as the thieves were somehow able to secure themselves sufficient time and privacy however, there are ways of penetrating just about any physical security.
But while you can't make it impossible for thieves to get in, you can make it impossible to get anything out intact if they don't use the proper access method. So long as its more important that the contents stay out of the wrong hands than in one piece, you setup a failsafe that will destroy the contents before an attempted break in can be completed. The technique also has the advantage of not requiring any staff to check on the security regularly, and so is good for security that will be unattended for long periods.
This is typically used to protect information rather than unique objects, as its easier to have a backup copy so that the loss of any single copy doesn't mean its lost forever. However it can also be found used with unique items that would be dangerous in the wrong hands, under the logic that its better for no-one to have it than the wrong people.
- n Season 4 of Burn Notice, an important MacGuffin is buried in a graveyard in an airtight container, which also contains highly reactive chemicals that would explode when exposed to the air. Filling the grave with machine oil allows them to get inside safely.
- In The Da Vinci Code, the cryptex protects its contents with a combination lock. Attempting to force the cryptex open will break the vial of vinegar inside, which would dissolve the papyrus along with its message before it could be read. As a result, only the right password will grand access to the message.
- In the videogame Uplink one of the security measures you can purchase for your gateway is a self destruct mechanism as a last resort if the Feds are closing in on you. You lose all the hardwear, but get to keep your reputation and avoid being disavowed (ie, gameover).
- The Holy Grail in Indiana Jones and the Last Crusade is protected by many layers of secrets, guards and traps. The final resort, however, is that the Grail can never pass beyond "The Great Seal". Doing so results in the entire place self destructing and the Grail being lost forever.
- Real Life Example: WW2 Uboat codebooks were printed on paper that would dissolve in water. Not only did this make the codebook easy to destroy, even if the crew were killed before they could, an attack on the sub would be very likely to cause the codebooks destruction anyway.
- The Matthew Reilly short story Altitude Rush (Available in pdf on his website) has documents protected by a self destructing case that will release hydrofloric acid on the papers unless properly accessed. The case also has an altitude sensor that will trigger the self destruct if it goes above 1000 feet or below 10 feet, necessitating the thieves to execute a frantic escape across the NY skyline.