Motion detector in hallway/entrance area

I thought the OP was about saving money... So far there are only a lot of (really good) tips, but all of them are significantly more expensive than plain switches.

The question is, what does a two-way switch cost, or what do you ultimately save if I have about 10 fewer two-way switches?

The question is what a two-way switch costs, or rather what you ultimately save if I have about 10 fewer two-way switches?

Question about the surcharge, not about the savings. Material = 1 motion detector corresponds to almost 10 two-way switches (depending on series/manufacturer). Additionally, somewhat less installation effort for the electrician.

But it's not always just money that plays a role. That has already been mentioned.

Price/performance candidates are the navigation lights, 3-pack online for €15, can be placed freely in the house without installation effort

In the old house, while sliding down the stairs at night, my wife tore her Achilles tendon, since then there is a prohibition on sneaking around in the dark at our place.

Savings. Material = 1 motion detector corresponds to almost 10 two-way switches (depending on series/manufacturer). In addition, somewhat less installation effort for the electrician.

That’s not entirely true... you have to take everything into account that belongs to it. A light switch does not only include the insert, etc., but also a drilled box, which then becomes unnecessary. The additional wiring for two-way switches should also not be underestimated (in terms of price). Roughly speaking, in a stairwell and passage rooms, the automatic detector is always worthwhile not only financially but especially because of the added comfort.