What task may alarm systems installers perform regarding mechanical security devices?

The correct option highlights that alarm systems installers are permitted to repair or service electronic access control devices. This points to the skilled nature of their work, where they are not only involved in the installation of alarm systems but also in maintaining electronic components that are integral to the security mechanism. It is essential for installers to have the ability to repair these devices to ensure ongoing security and functionality for their clients. This aligns with the expectation that qualified personnel should be well-versed in both the installation and maintenance of a range of security systems, including electronic access control, which often integrates with broader alarm system setups.

In contrast, the other options suggest limitations or specific actions that do not encompass the full breadth of what these professionals can do. For instance, solely installing new mechanical security devices does not address their capability for servicing existing systems. Monitoring mechanical devices may fall within other job functions but does not specifically apply to the role of installers. Selling mechanical devices without installation implies a separation from the installation task, which is typically part of their function. Hence, the focus on repair and service demonstrates the critical role these professionals play in maintaining the efficacy and reliability of security systems.