There is no such thing... I don't think the rules of frugality can be applied to health and safety issues. Actually if you are truly frugal than you value what is most important, so maybe over the top fire safety is frugal...
We have multiple floors, so we have multiple smoke detectors. By multiple I mean we have 3 on the first floor, 2 in the basement, at least 3 on the second floor & one in the attic. We also have 2 CO (carbon monoxide) detectors, although we have one that could be moved. We have 2 fire extinguishers, one between the laundry room and the stove the other upstairs in our bedroom. We will be replacing these this fall with bigger ones, they are also a little on the old side. I'm not sure how often you are supposed to replace them, but we've had them for 5 years, so I'm saying it's time to at least get a couple more!
We intend to add at least 2 more detectors to our array of protection as well. They will be the "Photoelectric" type. We will put one on each "living" floor. After watching a TV comparison that showed the photoelectric sensors detected a problem faster than the older model smoke detectors, we decided to add some. Faster is better, it means we have more time to get to safety.
We have just reviewed our fire escape plan with the children, we will do a drill sometime soon. Hubby just changed all of the batteries in the detectors. This is early for us, usually I schedule it for when we change the clocks for daylight savings time.
Am I paranoid, a little; overly cautious, you bet!!! Our community has had several fires in the last 6 months. We've taken a look at our house & our ability to react to the different causes of these fires. Our house was built in 1867, so it has it's own unique issues to think about as well. However, we have 2 modes of exit from the second floor, one directly outside, the other through our kitchen. The first floor has two doors outside. We have a meeting place that should be far enough away from the house to be safe and out of the way of where emergency personnel might need to be.
I have been slacking in the emergency kit department, time to get off my behind & get those up to date.
We started thinking about these things the same time we started preparing the furnace for it's first run. Of course having a fatal fire locally where the two victims were very close in age to my kids pushed us to be overly cautious, and added some extra steps to our overall plan.