The motivation of this research is to improve the ability of ambulation for people with a certain degree of disability. The control of the wheelchair is using two tilt sensors as an input-controlling module. One of the tilt sensors detects the anterior/posterior tilting of the head and moves the wheelchair forward/backward, the other distinguishes the left/right swing of the head. In order to increase the safety of this system, the M3S protocol established by the European Commission is also applied to this research. The system based on M3S protocol has the advantage of real-time signal transmission and emergent status monitoring for SCI patients with C2-C4 level. N the past the assistant device was designed with a unique connection, whereas a single input device was connected to a single output device which had neglected integral significance. These devices were not completely compatible with each other and had a rather poor integrated safety system. Furthermore, owing to severe degree disabilities who were quadriplegic from a cervical cord injury and had retained the ability to rotate their neck, were unable to switch arbitrarily between each connecting device by themselves, these one-to -one connected mechanism were not suitable for them. Therefore, it was extremely urgent to invent a connected interface and a simple input device for people with disabilities to operate in their wheelchair. In order to integrate different kinds of device and improve the facility of operation, Multiple Master Multiple Slave (M3S) is intelligent interface developed from European Community (EC) programs and individual people in the 90s. M3S protocol provides the standard interface between the input device and output device. A M3S system is based on the bus and devices. The bus of M3S contains three parts: 2 lines for digital communication (Controller Area Network bus, CAN bus), 2 lines for power distribution (Power bus) and 2 lines for safety features (Safety bus).