Well it "ain't that simple."
There has been cases when leaks quite some distance from the house has leaked along piping underground, and found it's way into a building through the piping entrance into the house.
Also, indoor piping is VERY low pressure, which in some ways makes it more dangerous. That is, a pipe cracked due to stress, earthquake, etc, may not leak right away, or may not leak all the time. Same is true for connections or valve packing. Normal "in building" pressure in the states is "quarter pound" AKA .25psi. Some commercial buildings run "half pound" and very large facilities can run "other than." .25psi is normally measured in the industry in "water column" that is 7" water column. A toy balloon likely generates more pressure
Also, some people are insensitive to the smell chemical added, and like any smell, if you start to experience the smell and don't recognize it, you become insensitive over time, and it can stronger and you not realize that.
None of these leaks of course "happen" yearly or on schedule.
I don't know what the answer is. Have your system serviced by a pro that you trust, and I used to do that "in a previous life." Without installing an explosive gases alarm/ monitor---which last I knew were quite expensive, your best defense is to "pay attention." If you think you smell something, you probably do. If you smell something and can't run it down, be INSISTENT. That has been a prelude to several explosions---"customer reported smell but cause could not be found" or some such
The only other solution I can think of, is to build your house/ building in such a way that the furnace/ piping is OUT of the house---a well ventilated "doghouse" on the side/ rear of the building.
These tragedies are like airplane crashes---they are sensational, but don't happen very often.
And often, you don't hear the details. Sometimes, possibly many times, these accidents are caused by "**** people do." I made one customer VERY angry one time, went down to do some sort of service, don't remember. But I DO remember---they had just moved in, and had an LPG dryer from their other house, and there in the basement was an LPG bottle hooked to the dryer.
WHY IS THAT DANGEROUS? Because LPG is heavier than air, and REGULATORS can leak. Gas regulators are required to have a safety vent in case the diaphragm ruptures, and either vented outdoors or in the case of a furnace or other appliance, be vented in such a way that the leak is vented into the combustion chamber via the draft air path.
Customers sometimes do all kinds of unadvisable stuff. Older equipment can be a problem. In the 80's--90's when I worked in the field, there were still a LOT of gas valve/ gas valve trains that did not have "100% shut off" safeties, meaning if the fire went out, the main burner valve shut down, but the PILOT light still sat there and leaked.........and that was perfectly acceptable back then.
I can still remember a service call early on a Monday morning. This was an older house downtown, been converted into legal? real estate? offices. The furnace was a "gravity convection" meaning no blower. Huge old thing down there with huge ductwork. It was overheating. The controls were all old--antique, really. The main gas valve---the one controlled by the thermostat, had failed---OPEN, and the stat had no control. Neither did the "high temp limit" as the valve was mechanically stuck, and out of the loop electrically. This was an INCREDIBLY simple system, and old----the old, separate "valve train." Main manual shutoff....the pilot gas valve, the pilot safety, and the "main operator" huge, motor powered.
Only reason it did not burn down, is the house was so old and leaky, and it was VERY cold weather, so it had the house up to maybe 80-85 and they finally opened the windows.
If it had been say, 35F outdoors instead of 3 POINT 5F it probably would have caught fire.
