New construction smoke alarms must receive their primary power from what source?

The correct choice indicates that new construction smoke alarms must receive their primary power from a backup battery. This requirement is crucial for ensuring the reliability and effectiveness of smoke detection systems in residential and commercial buildings.

Smoke alarms powered by a backup battery are designed to function even during power outages, which can occur due to various reasons such as severe weather, electrical failures, or emergencies. This feature ensures that the smoke alarm remains operational at all times, providing a critical safety function by alerting occupants to smoke or fire, regardless of the building's electrical status.

While some smoke alarms can be wired into the building's main power supply, the inclusion of backup batteries is essential to ensure continuous operation. Therefore, the primary power source is not just about being connected to the main supply; it must also have a reliable backup to maintain safety standards.

Other energy sources mentioned, such as solar power and wind energy, are not common for smoke alarms because they typically require more consistent and reliable energy supply than what these renewable sources can often provide for continuous operation.