Will directv id card work in other directv cable boxes that are not my own?

No. They will not due to the receivers being linked to a specific account number. This account number is called a CID. The CID is actionable to a specific lease agreement, that is specific to the receivers it was created with. The receivers have RID #'s (Receiver Identification Numbers) and they function hand in hand with Card Access #'s. The id card you question about, is the link between your account and what the receiver is able to access for you, and it will not work on another's cable box because it is linked to another account.