Installing smoke detectors is mandatory

No matter whether networked or not, I bet you hear the smoke detector!

I disagree. We had that situation just a few weeks ago. False alarm from the detector in the hallway on the ground floor while sleeping upstairs in a room with the door closed. You could hear something, but everyone (!) in the house thought it was the alarm of a car parked further away. It only became clear the next morning. Now one could say, you woke up and then would have noticed the smoke. Or maybe not... So far, we have kept networking open but are leaning at least toward partial networking across the floors.

I got the fire detectors from the company He***ron. According to several acquaintances (including firefighters), they have the lowest rate of false alarms and are considered very reliable.

In the basement hallway, ground floor, and upper floor, as well as in the utility room (in the basement) and the attic, there are 5 wirelessly networked units, and in the living room as well as all bedrooms, we have non-networked detectors, also from the company.

This way, in an emergency, you would be immediately alerted in all bedrooms if there is a fire there and you are currently present. If there is a fire in one of the passage rooms, i.e., in the escape routes, the whole house would beep, no matter where you are. And if you happen to be in the living room and there is a fire in one of the bedrooms, you would also be alerted.

The utility room in the basement with all the technology is connected separately by wireless, as I consider this to be the biggest fire risk after the kitchen. And it is located furthest from the bedrooms.

You could at least install simple detectors for the upper floor hallway and all bedrooms first and later retrofit wireless ones for the more distant rooms.

Our first smoke detectors were from Ei Electronics, which communicated with each other via cables (I believe wireless was not available back then). Now I have replaced the long expired ones with new ones, which are the EI650C-D mentioned by dab_dab. Since the cables were already in place, wireless was, of course, discarded. As one of the 10 smoke detectors is installed in the basement, it probably wouldn't be heard easily through a closed door on the first floor. Therefore, I would always connect the detectors with each other using cables.

Five are networked with us via radio: hallway+hallway+roof+kitchen+utility room, the others are not. I also have those from Ei. Don’t buy anything cheaper, after the first false alarm at night money won’t matter to you.

In addition, you can also integrate the Co detector with the EI devices, which is very useful for combustion heating appliances (gas boiler / wood fireplace / etc). I have also linked my alarm system with the smoke detectors and they thus serve as indoor sirens.

I think you can also overdo it. When you think back to the old days - it might still make sense to link the electric blinds so that they open at night and all the lights in the hallway come on, thus illuminating the "emergency route".