In this work, a solution to monitor users’ activity within an indoor scenario is proposed. It is based on non-wearable and non-invasive sensing, and it is specially fitted for the elders’ home monitoring. The localization of a person is estimated through an optical sensing network that detects the floor vibration produced by the footstep when walking. Optical fiber Bragg sensors are integrated within high sensitive accelerometers to detect such vibration. Three similar accelerometers were developed from which sensitivities of 269 pm/G, 225 pm/G, and 209 pm/G were found. Allied to vibration detection, an algorithm is employed to retrieve one’s position from the data. In preliminary localization tests, the system has demonstrated an accuracy under 5 cm over a 3.2 m2 detection area, proving itself to be a promising solution for the targeted application.