Techniques for authenticating users at devices that interact with the users via voice input. The loop members are adapted to assume a deployed position in which one loop member is disposed at an angle with respect to the other loop member at the overlapping points, so that the structure defines a top side, four vertical sides, and a bottom side when in the loop members are in the deployed position. This transmittal includes incorporating the PIN number in an electronic mail message. The retention apparatus includes a securing structure configured for being wrapped around the insulating body to secure the insulating body in a fixed position with respect to the firearm sound suppressor after the insulating body is wrapped around the firearm sound suppressor.