You might consider one of the small, lightweight, single burner butane stoves. These still have the issues of CO if you're using it in your garage. I used this for a 5 gallon extract brew and it worked great. As below I left the garage door open during the boil.
As with anything it comes down to common sense and following basic safety guidelines. I personally use a propane Camp Chef high pressure burner for mashing and the boil of my BIAB. When I brew, I brew in the garage/driveway. I place the burner just outside the garage door in the driveway with the propane tank sitting outside of the garage as far as the hose will allow (keep in mind the high pressure stoves have very short hoses). I leave the garage wide open (during mash and boil) and of course stay with it for the entire time. Once I'm finished with this part of the brew process or don't have the flame on, I turn it off at the propane tank in addition to the stove on/off controls. Once I'm done I disconnect it, and store it in the outdoor shed that is well ventilated.
I'm curious @sneezles61, how many watts do the electric brewing systems use?