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