Smart home without switches? P.Hue, Home Assistant, Homematic wired IP

For access to the apartment, Bush Jäger offers a smart lock, while Nuki is linked to a cloud service for management......how does Bush Jäger handle this? Is it designed to also authorize external persons legally? How do they then gain access?

Isn't the Busch Jäger system just a disguised KNX? Such routines can be created via IFTTT. I am sure, however, that there is already ready-made software for holiday apartments, hotels, etc. Theoretically, in such a case, linking via voice assistants is also sufficient. Hue, door lock, thermostats, light scenes. That would be the simplest. I hope that was sufficiently constructive. Nevertheless, I would like to point out again the separation of networks. If you do not do that, you will quickly come into conflict with the law in rented apartments (data protection, etc.). I am a fan of pragmatic solutions, but with rented properties, you should not act hastily.

A note on DLAN; if the apartments are supplied via (V)DSL: never. That will cause interference and disconnections both in the home network and, if things go badly, with the neighbors. They will not be pleased..

One possibility would be to use the FritzBox as a router for both networks and to create a separate WLAN network for each apartment. For this, I could create two different WLAN networks with different names and passwords in the settings of the FritzBox. Or? At least that would be solved then.

No, the Fritzbox is not VLAN capable. You do have two WiFis then, but the networks have access to each other. And no, the DLAN solution is useless. You are just inviting problems into your home. A good repeater solution is even better.

You might want to switch from just skimming through some websites to an intensive technical engagement. There is currently still a lot of guessing and hardly any knowledge going around.

One possibility would be to use the FritzBox as a router for both networks and create a separate WLAN network for each apartment. For this, I could create two different WLAN networks with different names and passwords in the FritzBox settings. Right?

At least that would be solved then....

Nothing is solved because a FritzBox can’t do something like that. If you want to do it properly and want external access to both networks while they don’t see each other, you either need a dual-WAN router in each apartment or you build it with a managed LAN with a capable router and VLANs.

And I think that looks really neat. devolo 1200 DINrail- Gigabit-Internet from the distribution box| devolo

Powerline networking never, under no circumstances, ever looks neat. It’s at best an absolute emergency solution when nothing else is possible.

What is your technical background regarding electrical and network technology as well as Linux, etc.? Especially if it’s about connecting the booking system and fully automatic "starting up and shutting down" the apartments, you are either in the professional hotel segment (look at Sauter...) or can program intensively yourself. For things like "I want to see if people are in the apartment," I would be extremely cautious if it goes beyond "is it booked or not."