Can be achieved by placing different Tech style furniture pieces, it doesn't matter what type (can be kitchen, chairs, art) as long as it has the Tech indicator in the game.
More Tech furniture will unlock while researching different things at the decoration shrine and you will also be able to unlock some Tech furniture via friendship levels.
The game will state if you already have 1 of an item and that the stats won't go up, i.e.; have 2 Tech furniture of Tech: 2 stat, is not 4 stat, it's 2 stat.