*2.2. Sensing Position*

The sensor placement highly affects the detection performance. Previous studies [14,33,34] demonstrated that better results are achieved when sensors are placed along the longitudinal axis of the body (e.g., head, chest, waist) when compared to other placements (e.g., thigh, wrist). The movement of this axis during a fall is more consistent and steady. However, this requires to wear a dedicated device on uncommon body parts which consequently creates inconveniences. For this reason, other studies [11,28,29] used commodities (e.g., smartphones carried by the thigh, smartwatches worn on the wrist). These usually do not disturb the users since they already wear them. However, people tend to take these devices off when they are at home which makes the FDS useless. Another method is to combine various sensing positions. Özdemir et al. [27] developed a system consisting of six wearable devices that are all used together. The problem is that the elderly already have acceptability issues with one device, let alone six.
