I have one. It does work, and can distinguish between smoke and CO alarms. You only need one if you have interconnected hardwire alarms; you won’t be able to tell which specific floor it starts from.
No batteries needed, same function, and while I haven’t had any reliability issues with the sound detector I figure the hardwire one is likely more reliable. I just installed one a couple weeks ago, very simple, now I have two detectors.
I have one. It does work, and can distinguish between smoke and CO alarms. You only need one if you have interconnected hardwire alarms; you won’t be able to tell which specific floor it starts from.
A newer solution would be this: https://www.getzooz.com/zooz-zen55-dc-signal-sensor/
No batteries needed, same function, and while I haven’t had any reliability issues with the sound detector I figure the hardwire one is likely more reliable. I just installed one a couple weeks ago, very simple, now I have two detectors.