Why were combination locks considered especially secure for safes and strong-room doors?

Combination locks became the most secure form of closure for safes and strong-room doors during the late 19th century for several key reasons:

• Immense Complexity: They offer an almost infinite number of possible combinations of letters or numbers, making unauthorized access statistically improbable.1
• Lack of Keyholes: Unlike traditional locks, they do not have keyholes. This design feature is critical because it eliminates the vulnerability of having an opening where an explosive charge could be inserted to blow the mechanism apart.1
• Ease of Manufacturing and Use: They are relatively simple to manufacture and allow for the combination to be easily changed, providing flexibility for security management.1

By requiring the alignment of internal slots through a specific sequence of dial movements, these locks ensure that the bolt mechanism remains secure until the precise combination is entered.1