We have developed an optical fiber network combining communication and sensing using a hetero-core spliced fiber optic sensor inserted into an existing communication line. The measurement uses the Internet infrastructure effectively, and the sensitivity characteristic by wavelength of the measurement was examined. In addition, six binary switch modules and one displacement sensor module using the hetero-core spliced fiber optic sensor were inserted into an actual communication line, and the influence on the communication was examined. The hetero-core spliced fiber optic sensor showed the characteristic of loss only. When the sensor is inserted into the communication line, if the loss can be controlled to within tolerance to the wavelength of 1.31 μm of the communication line, a measurement function can be added to the communication line by a comparatively simple construction method. In addition, we realized a multiple binary switch measurement in real-time basis with tandem connection by simple addressing algorithm. The binary switches can be applied to a home security system to monitor the state of doors opening and closing. We have successfully fabricated and demonstrated the binary switch sensing system with tandem connection consisted of three binary switches using the proposed method.