Grid ceilings in buildings have many forms, but the installation of photoelectric smoke detectors do not have the requirements in our related standards, and it is difficult for the fire department to design, supervise and inspect. So the installations of fire detector are different for different places, on the grid ceilings or building roofs. This will lead to some problems. On the one hand, detectors can’t realize early detection and may have blind spots. On the other hand, full coverage of detectors will lead to large investment and financial waste.