Smoke and CO detectors

Hardwired and connected across the home.
Hardwired power
Review the existing detector wiring and the devices already connected to it before choosing replacements or additions.
Interconnection
Plan the devices as one warning system so an alarm is not limited to a single location.
Placement for the home
The layout, levels, rooms, and existing system all belong in the placement conversation.
Review the whole system before changing one device.
List the existing devices
Note where detectors are installed, which ones are hardwired, and whether they currently sound together.
Walk through the layout
Review the levels, sleeping areas, and other relevant spaces without relying on a one-size-fits-all diagram.
Plan compatible replacements
Bring the available device information so the existing system and proposed replacements can be considered together.