Our online shop has photos of all equipment installed in your home. Central unit and control relays are installed in your electrical center. There they are not visible, and look like industrial electrical components.
The only visible devices are room temperature sensor(s) and possible air-to-air heat pump controller(s). The come with plastic enclosures designed for residential use. If you wish, you can hide also them e.g. above or behind furniture, as long as you make sure with the installer that the location is suitable.