HUD Key Codes
an excerpt from:
Once you have removed the old locks as directed by your work order, you will install new locks that have specific key codes. Not all locks are necessarily changed. You may change only a secondary door, only the front door or both. The locks that are to be changed depends on a couple of things such as if the foreclosure process has been completed or if the foreclosure process is still in the works. Your work order should specify which doors are to have the locks changed.
The locks to be installed have specific keys that must be used and the keys are identified by a number, such as 32541, 44535, 76667, etc. You will be told which lock to install or the standard for your area will be made available to you in your work order or client procedures manual.