US Patent 7917263 Activation system and method for passenger protection device

An activation system for a passenger protection device comprises a pair of communication wires, a central unit for detecting currents flowing in the communication wires, and a satellite unit for varying the currents flowing in the communication wires based on output data of an acceleration detection sensor. The central unit calculates a sum of the detected currents and compares the sum with a first predetermined level to detect the output data of the sensor. The central unit also calculates a difference between the detected currents and compares the difference with a second predetermined level, thereby detecting failure in the communication wires and stopping activation of the passenger protection device.