What is the purpose of the Switch Indicator Module (SIM100)?

The SIM100’s purpose is to deliver switch status over an NMEA 2000 network. Because of this feature, the use of common end of line components is available. The most common of such components are normally closed switches, such as magnetic door, window, and hatch switches used in most alarm systems for homes. The SIM100 also makes it possible to connect several normally open devices, for example: monoxide, bilge level, motion, and smoke detectors. 
Please refer to the SIM100 manual for further details.