A phylactery of faithfulness was a small black box containing religious scripture, tied around the forehead by a leather cord. There was no way to determine precisely what function it performed until it was worn.
Despite their usefulness, phylacteries of faithfulness were among the simplest and cheapest magic items to manufacture, available to virtually any divine magic spellcaster who could create wondrous items. To create a phylactery of faithfulness, the creator must cast detect evil, detect good, detect law, and 'detect chaos during the process.
If the wearer of a phylactery of faithfulness took a moment to contemplate an action or item that may adversely affect his or her alignment and/or standing with their deity, he or she became fully aware of the consequences before performing the action.