The utility model relates to an antitheft system in a large area. The system comprises two parts, namely sensor submachines and an alarm host-machine. The sensor submachine sends an alarm signal by the utilization of a superregeneration wireless signal; and the alarm host-machine receives the superregeneration wireless alarm signal and then dials the mobile phone of related personnel and sends an alarm text message through a GSM network, and also can drive an audible and visual alarm. As transmitting distance of the superregeneration wireless alarm signal is only hundreds of meters, the sensor submachines adopt a relay communication mode. That is to say, each sensor submachine can send a superregeneration wireless alarm signal and also can transmit a superregeneration signal sent by a close submachine. When the superregeneration signal is sent to a receiving range of the alarm host-machine, the alarm host-machine can respond to an alarm signal of the sensor submachine. By miniwatt open wireless frequency band and relay communication, long-distance wireless transmission of an alarm signal is realized so as to achieve the effect of antitheft alarm within a large area.