Top features: - Reactive monitoring helps to keep your home safe - Smartphone alerts let you know what's going on - No more annoying alarms Reactive monitoringYour safety matters. That's why the Nest Protect Second Generation Wireless Smoke & Carbon Monoxide Alarm is the first smoke alarm that can detect any type of fire.The Split-Spectrum Sensor inside the alarm analyses two different light wavelengths to recognise both slow- and fast-burning fires.This smoke and CO2 alarm tests itself constantly, so you won't need to worry. You can see it's working at a glance - it provides a green glow when all of your Nest Protect alarms have tested themselves.Smartphone alertsYou should always be in the know, so the Nest Protect has a Heads-Up early warning function. It sends you a message on your smartphone or tablet it detects smoke, or if carbon monoxide levels are rising, so you can take action.The alarm has yellow lighting when it detects danger, and speaks with a human voice to let you know