Replace Nest Protect's batteries - Google Nest Help
Google Nest Protect Smart Smoke and Carbon Monoxide Detector Alarm (Battery) in the Combination Smoke & Carbon Monoxide Detectors department at Lowes.com
The Best Smart Smoke Alarm | Reviews by Wirecutter
Life with the Nest Protect: Are “smart” smoke detectors a dumb idea? | Ars Technica
Google Nest Protect - Smoke Alarm - Smoke Detector and Carbon Monoxide Detector - Wired, White - - Amazon.com
Replace Nest Protect's batteries - Google Nest Help
Nest Labs 06A Nest Protect Battery-Operated Smoke Alarm + CO - White | eBay