The invention discloses a smart home security system, which solves the problems that the monitoring clarity and sensitivity are low and there is no intelligent preventive measures when a fire danger occurs in a room in the prior art. The smart home security system comprises a PC, a wireless network module, a camera, infrared detectors, smoke detectors, a gas detector, buzzing alarms and automaticdoor closing devices, wherein each automatic door closing device comprises an outer housing, a movable lever, lever supporting seats, electromagnetic blocks, a door mounting seat, a cylindrical spiralcompression spring, a compression spring, a normally moving piston rod, a fixed piston rod, piston cylinders, a mounting seat, a permanent magnet and permanent magnet blocks, the magnetism of the bottom end of the permanent magnet block is different from the magnetism of the top end of the corresponding charged electromagnetic block, and the compression spring is in a compressed state after the permanent magnet blocks are attracted to the electromagnetic blocks. The smart home security system is simple in structure, scientific and reasonable in design, convenient to use, high in monitoring clarity and high in sensitivity, and can automatically close the door when a fire danger occurs in the room so as to insulate the fire source.