A self-expiring access code refers to a PIN code that is generated for a smart lock. In order to control who has access to specific spaces and when, access control software allows you to set exact times for when the PIN is valid. For example, you might generate a PIN code for a plumber to work at your property, but specify the time it’s valid from 8 a.m. to 12 p.m., when the PIN automatically expires and won’t unlock the lock.