What advantage do hard-wired smoke detectors have over battery-operated ones?

Hard-wired smoke detectors offer the significant advantage of providing continuous power and the ability to be interconnected with other alarms in the system. This ensures that when one smoke detector is triggered, all interconnected detectors will sound, providing an enhanced safety measure throughout the entire area, especially in larger spaces or multi-level homes. Continuous power reduces the risk of failure due to dead batteries, which is a common issue with battery-operated detectors. Additionally, hard-wiring ensures that the smoke detectors are always ready and functioning, critical for early detection of smoke or fire.

The other options, while they may have some truth in different contexts, do not define the primary benefits of hard-wired systems as effectively as the interconnectedness and continuous power do. The installation cost can often be higher for hard-wired systems, they might require more regular maintenance due to their electrical components, and relocating them can be more complicated compared to simply moving a battery-operated unit. Thus, the strength of hard-wired smoke detectors lies primarily in their reliability and integrated safety features.