Motion sensor as fire alarm?

I’m going to build a basic woodshop in my tiny 1-car garage. In a woodshop you have to use a heat detector instead of a smoke detector, because sawdust floating in the air can trigger a false alarm on a smoke detector. I’ve run across mention somewhere (I think on a woodworking forum) about using a motion sensor as a fire alarm.

I assume the motion sensor is just an IR sensor and either fire or a warm body triggers it. Is anyone here doing this, and if so, do you just use a “motion” event or do you pair it with a temperature reading (for example, from the ST Multi-sensor or from the Monoprice Motion/temp sensor)? Or do you just assume, for example, that “motion” detected in the garage at night or when you’re not home could be either a fire or a burglar?