Google Nest Protect (Battery) vs Heiman Smart CO Alarm

Sensor depth wins this round: the Google Nest Protect (Battery) comes out ahead overall, detecting both smoke and carbon monoxide alongside occupancy, temperature, humidity, ambient-light and motion sensing, features the CO-only Heiman Smart CO Alarm simply does not have, plus self-testing, an automatic pathlight, and steam-check tuning. The Heiman Smart CO Alarm keeps pace on price, a battery rated to last far longer between changes, and broader integrations, reaching Google Home, Alexa, Apple HomeKit, Samsung SmartThings and Home Assistant through Matter over Thread, versus the Nest Protect's Google Home and Home Assistant support. The two also serve different purposes: the Nest Protect is a full smoke-and-CO alarm meant to replace your primary detector, while the Heiman is a standalone CO monitor best paired with existing smoke coverage. Households wanting one premium alarm that handles smoke, CO, and a deep sensor suite should get the Google Nest Protect (Battery), while budget-focused buyers who just need a long-lasting, widely-compatible CO monitor alongside smoke detectors they already own should pick the Heiman Smart CO Alarm.