NIS - 07 ion smoke sensors have an ionization chamber, the ion chamber used artificial radioactive element americium 241 (Am241), the intensity of about 0.8 micro Curie, under the normal state is in the balance of the electric field condition, when there is a smoke into the ionization chamber, ionization produced positive and negative ions, interfere with the normal movement of the charged particle, under the action of electric field, respectively to the positive and negative electrode, destroyed the balance between the internal and external ionization chamber, current, the voltage will change. Ion smoke smoke sensor is through the equivalent resistor voltage changes due to ionization chamber to perceive micro electric current change device of smoke particles. To macro performance for the equivalent resistance of ionization chamber increase causes the voltage at the ends of the ionization chamber, thus to determine the status of the smoke in the air.