Abstract: In a method and apparatus for securing car against theft via wireless sensor, a charging circuit and chargeable battery, a CPU circuit connected to a transmission circuit, and an air pressure sensor or an infrared sensor are provided in a cigarette-lighter plug, so that the sensor detects any change of air pressure or any change of temperature in a car due to any invader, and sends a trigger signal to the CPU circuit. The signal is encoded at the CPU circuit and then transmitted via the transmission circuit to a wireless antitheft main unit mounted in the car to trigger a siren as a warning if main unit is set to active stale by external remote control transmitter. Since no wire is needed between the sensor and the main unit, a thief is prevented from locating the main unit by tracing any wire extended thereto.