Smoke detector: In which rooms is it really necessary?

There are special regulations for this.

Some time ago I also replaced our smoke detectors that were more than 10 years old.

The new ones are from the same manufacturer as the old ones and are again connected to each other by wire since the cables were already in place.

The detectors are powered by 9 V batteries.
I am not enthusiastic about the permanently installed batteries.

Costs:
Smoke detector approx. €19
If a radio module is desired, then another approx. €31.

So together approx. €50 each.

I think laying cables is cheaper, especially if you do it yourself, which is not rocket science. Attaching the detectors can also be done by yourself.

I hijacked your list and marked in red where I disagree with your statements. But that is just my opinion.

OG: Child1 (1), Child2 (1), Bedroom (1), Dressing room (accessible only through the bedroom) (0), Hallway OG (1) Staircase (1)

EG: Kitchen (0), Dining area (1), Living area (1) (both rooms combined into a relatively large living space of approx. 62m2 that is not separated from each other), Bathroom EG (0), Pantry (1?), Hallway EG (1) Staircase (1)

Basement: Technical room (1), Laundry room (1?), Storage room (currently simply an empty room intended for things to be stored, bicycles, items to keep, etc.) (1), Office (1)

By pantry, the pantry room is probably meant. If a chest freezer or something similar will be placed there, I would also install one there.

Hallway and staircase. Are these separate from each other? If yes, then I would probably install one in both the hallway and the staircase; otherwise, one on each floor should be sufficient.

There should be no smoke detector in the kitchen but rather a heat alarm.

Depending on the heating system, I would also install a CO detector.

And yes, the devices should definitely communicate with each other so that if one detects something unusual, all the others make noise.

Now I am curious whether the OP will comment on this topic again.

The problem with smoke detectors without permanently built-in batteries is the sensor, which does not last forever. Better to replace them completely every 10 years than to eventually have a smoke detector on the ceiling that no longer works.

I don't understand your post.

Do you mean that the infrared diode or photodiode is better in a smoke detector with a built-in battery than in one with a replaceable battery?

That is probably not the case.

By the way, smoke detectors have an expiration date. They should be replaced after 10 years anyway.

I don’t understand your post.

Do you mean that with a smoke detector with a permanently installed battery, the infrared diode or photodiode is better than with one with a replaceable battery?

That’s probably not the case.

By the way, smoke detectors have an expiration date. They should be replaced after 10 years anyway.

He probably means that smoke detectors should be completely replaced every 10 years anyway (as you also wrote), because the sensors reach the end of their lifespan then. Thus, one can also use smoke detectors that have a 10-year battery. This eliminates the need to change the 9V block. Whether those with a fixed 10-year battery actually last 10 years remains to be seen.