But you STILL need a CO detector inside.
It's certainly a good idea, but I don't think it's required. At least not around here. All the homes I've been in over the years that had gas stoves did NOT have a CO detector. Of course, the CO detector is a relatively new phenomenon on the market, having come around in the last 10-15 years. When I grew up, those and even smoke detectors weren't around.
I have a ventless gas fireplace - no CO detector came with the house despite that, though I bought one as I'm a little suspicious of ventless fireplaces.