First job I had, there was a keypad to gain entry to the "secure" area, guy came to service it, told the boss it was fine but we needed to change the code as he had guessed it straight off (1066). Next time he came guessed the new code straight off (6969), apparently they were the most common security codes back then 1990s
I worked in a pub many years ago and we had an issue with the alarm. The Brewery sent out an engineer (alarm technician) to sort it out and used 1515 as the code which worked. That was apparently a well known number used in the trade at that time.