The building that Li Yao had asked for from Jin Yuyan was one of the communication nodes of the Business Alliance of Ten Thousand Sectors in the first place. The Business Alliance of Ten Thousand Sectors had a business network all over the center of the cosmos. Naturally, they boasted state-of-the-art communication equipment. Also, after retrieving abundant magical equipment units from the Business Alliance of Ten Thousand Sectors' warehouses, Li Yao crafted a few enhancement and blockage devices himself, finishing the modification on the super-remote secret communication system.
Both Jin Yuyan and the four families could've monitored their communication. However, the messages that Li Yao sent out detoured in seven Sectors countless times before they were delivered to the flagship of the "Coalition Fleet of the Pyromaniacs". They were also blocked, encrypted, and anti-tracked by Xiaoming and Wenwen. It was absolutely impossible for other people to detect them.
