I think the Bramah Lock probably holds the record for going the longest time as "unpickable" (1784-1851) until AC Hobbs did the trick. http://mentalfloss.com/article/50182...npickable-lock

I don't think there is a truly unpickable lock. As pointed out though, at some point it becomes much easier to go through the door, window, wall, floor, or ceiling than to mess with the lock.