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Learn about Nest Protect's Split-Spectrum Sensor

The 2nd generation Google Nest Protect uses an advanced smoke sensor, called a Split-Spectrum Sensor, to detect a wide range of smoke events, including slow, smoldering fires and fast flaming fires.

Since the 1970s, home fires have changed: while it used to take up to 30 minutes for a fire to take over a room, it would take less than 5 minutes today, because home layouts and furnishings have changed. Yet, most smoke alarms have relied on the same smoke sensors for the last 40 years: photoelectric and ionization.

According to the NFPA, photoelectric sensors are generally understood to be superior at detecting smoldering fires, while ionization sensors are perceived to be better at flaming fires. However, ionization sensors are also prone to nuisance alarms and contain radioactive materials like Americium-241.123

The 2nd generation Nest Protect uses a different approach: a completely re-designed Split-Spectrum Sensor that looks for both smoldering and flaming fires. The Split-Spectrum Sensor enhances a traditional infrared photoelectric sensor with a second, blue LED, to detect a wider range of particle sizes in the air. While this technology has been used in commercial grade alarms, it's not currently used in residential alarms.

How the Split-Spectrum Sensor Works

Like a traditional photoelectric alarm, the Split-Spectrum Sensor has an 880nm infrared wavelength that looks for large particles created by slow smoldering fires.

A second, 450nm wavelength of light looks for the tiny particles created by fast fires. The shorter wavelength acts like a fine tooth comb, which allows the sensor to detect smaller particles more easily than a longer wavelength.

Being thoughtful means more than just alarming at the right time — it also means staying quiet when there's not an emergency. The Split-Spectrum Sensor is shielded against outside light and encased in a stainless steel screen. The screen's hexagonal pattern is designed to let smoke in and keep bugs and fibers out.

Interested in learning more? Read the Split-Spectrum Sensor white paper.


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