A few questions in regards to Disable Device:
Check: When disarming a trap or other device, the Disable Device check is made secretly, so that you don't necessarily know whether you've succeeded.
So the GM would do the role for the PC?, the PC is not aware of the roll result and obviously not the traps DC.
The DC depends on how tricky the device is. If the check succeeds, you disable the device. If it fails by 4 or less, you have failed but can try again. If you fail by 5 or more, something goes wrong. If the device is a trap, you trigger it. If you're attempting some sort of sabotage, you think the device is disabled, but it still works normally.
Following the train of thought the PC is unaware of success or failure, How does the PC know if they should try again or not? Obviously if the player fails by 5 or more the trap goes BOOM!! thats a rather good indication of failure. If successful or failing by 4 or less nothing will happen?