I have a halo and I like it. It can work on its own via WiFi, or paired with ST via Zigbee (but not both simultaneously).
I also have two battery-powered ZCombo smoke/CO detectors paired to my ST hub. These are z-wave devices. I replaced one of them when it falsely detected smoke on two separate occasions. Could have been something simple like dust or something, but I didn’t want to take any chances so I bought another one.
Then there’s Leeo, which isn’t a smoke/CO detector at all. It’s a small device that plugs into an outlet and listens for the pattern of a smoke or CO alarm going off (the pattern of beeps is standardized in the US), then you get an alert from their app, which includes a recording of what it heard, and the same thing with a phone call. It doesn’t integrate directly with SmartThings but they have an IFTTT channel so it’s acrually possible to integrate indirectly.
And lastly, I have one dumb wired smoke detector with a relay that connects to the interconnect wire; the relay has outputs that can be wired to some z-wave contact sensors. So if the detector goes off, the contact sensor closes and you can get an alert in ST. Both kidde and first alert (BRK) make a version of this relay device for use with their detectors.
There are a few threads that discuss how to do this in more detail. This is a relatively recent one, with a nice step-by-step write up.
I have all of these setup because with remote monitoring for smoke/CO, I think it’s important to minimize both false alarms and failure to detect smoke/CO. With several redundancies, I’m less worried that a single failure point will mess everything up.
These are all good options. The bottom line is, pick something and install it. As you’ve already pointed out, you are at risk because there’s currently no smoke/CO detector installed next to your bedroom.