Good question @thebird! The Listener is able to listen for both smoke alarms and CO alarms. If you are wanting the one Listener to account for both Alarm types, this will depend on placement and testing.
To start, you will want the smoke alarm and the CO alarm to be within inches of each other as well as the listener microphone facing both. Next, you will want to go through the Listener’s test mode and sound the smoke alarm and co alarm during the same testing window, or one immediately following the other. Let us know how this goes! 