Actually our building is much older...But as written elsewhere, we had to renew everything anyway. I used Homematic before switching over to KNX (/KNX:RF) and while it was okay for a rental (and can do much more than people think) it's still clunky unless you use HA as an additional layer and you waste a lot on batteries. But still, better than nothing.

We are lucky that we actually have the best renters we could ever imagine but their flat was renovated cabling wise before we bought the object so there was little use of implementing something that would require rewiring AND puts me deep in the "functional liablity and GDPR" hole. But if I ever need to rewire it, it will be done with KNX simply because I can do that myself. German/GDPR law sadly is a bit uninnovative in that regard - I would happily offer my renters fingerprint access but the fact that I then would need to do four different data transfer aggreements is a hard reason to not do it.

When renting out you very soon find out that the law is heavily geared towards big corperations like vonovia and fucks over the smaller landlords whenever possible, sometimes even to the disadvantage of the renter. E.g: I can easily produce heat consumption directly from the heating system for each renter, even can automatically send them this. It can hardly be manipulated and is seen as evidence in other countries.. BUT: As we rent out two apartments I do not fall under the "small landlord clause",even though the smaller one is just a studio. So I need to install a wireless heat measuring system on all radiators and warm water outlets. Now here comes the problem: These measuring devices need to be capable of wireless measurement soon. Funny, as all of them are in the same room...where the heater is. right next to the gateway.

But you need them by law and now I need to put this shit on my renters side costs... almost 25€/month (and that was the cheapest offer by far) per apartment. I rent out for somewhat reasonable prices (well below Mietspiegel), as I rather have friendly renters than max out what I get...but that shit makes me mad. (We "refinanced" it by me taking over smoke detector maintenance so we could keep costs the same)