One Link 2In1 Smart Smoke Carbon Monoxide Alarm, Alerts You To Both Types Of Danger In Your Home, Sends Emergency Notifications, Via Your Phone, While Voice Alerts Tell You The Type Location Of Danger, Interconnects With Other One Link Devices Sold Separately To Create A Smart Home Safety Network, So If One Alarm Sounds All Will, Works With Amazon Alexa So You Can Ask Alexa To Check The Status Of Your One Link Alarm, Hardwired Alarm Includes An Adapter Plug So You Don’t Need To Rewire, A 10 Year Sealed Battery Backup For Protection In Power Outages, For Maximum Protection, Hardwired Alarms Should Be Installed On Every Level Of The Home Inside Each Sleeping Area