Related Clues:

• They may be hard to crack
• Places for rings, maybe
• They may be cracked using stethoscopes
• Man following company rules
• Morse and others
• Jewel cases?
• Programs
• They may be blown or cracked
• Does some computer programming
• Vaults for valuables
• They're still often dialed
• Hiding places in walls
• Money holders
• What walls might hide
• Cracksman's targets