Nest’s smoke alarm features a voice alert that gives users an early warning. The split‑spectrum sensor uses two wavelengths of light to detect smoke from fast-burning and smoldering fires. It checks its batteries and sensors over 400 times a day and quietly tests the speaker and horn monthly.

Kidde’s sealed lithium-ion battery-powered smoke alarm uses ionization-sensing technology. It may detect invisible fire particles that are associated with flaming fires sooner than visible particles. It is tamper- resistant, has an alarm memory and a flashing red indicator LED with four modes of operation.