But more curious. Why did the use this system, back then when building those (low cost I think) houses. They could save on high voltage wires and switches, but also need to add those relay boxes. The 'doorbel' style switches where not durable, as many where replaced, by new ones, many different styles

I did not see the relay boxes inside, but from its function it must be ímpulse' relays.Those boxes looked like small cast-iron installation cabinets, one on each floor, with many layers of paint on them

Does anybody know those systems excisted for normal houses, and what could be a reason to build it that way? Would it be cost, or would it be some 'modern' thing for that time? Or was it used for some kind of renovation, where no tubes for wiring needed to be deployed into the walls? The switching wires where just tiny cables cramped to the door-frame.