I use [Home Assistant] on a NixOS server at home.
Home Assistant is an open-source home automation system, designed to be a central control system for smart home devices with a focus on local control and privacy. It's implemented in Python and has a bewildering array of integrations, so in turn it has a huge number of depdendencies!
There's a great [Home Assistant NixOS module] that allows declarative configuration of Home Assistant.