Except they thought the attack would be in the Philippines! Pearl Harbor was far to bold to consider.
If the earlier movie about the Pearl Harbor attack is somewhat true, we had radar on Hawaii but it was relatively new and the indications were not fully trusted, either they thought they were supply planes, or just didn’t believe what they saw. Radar was really know, though the Brits used it a great deal in 1940 to track and repel the Luftwaffe.