4 digits for radio is OK , Who wants to click a lot of numbers
Radios allow over 65000 combinations not 9999.
...
Assuming you can try 1 number in 7 seconds for every hour of work you would have 5% chance to open the safe. Unless the number can be changed and owner does it regularly (ideally every day) the number adds up and you can be 100% sure that after 20 hours of work (no necessarily continuous, can be done 1h/day) the safe is compromised (but it's equally possible that it will take less than 10 hours than more).
...or change the code often).
Unless the number can be changed and owner does it regularly (ideally every day).
Dynamite isn't that good thingy to open the safe. At least if you care about items that are inside it.
... change the code after each closing of the safe and telling the new number into the players messagebox.
Who wants to click a lot of numbers