2) Accelerometer: is an instrument that measures the applied acceleration acting along the sensitive axis [18]. It is widely used for human activity recognition purposes [19 -21] because of its capability to respond to both frequency and intensity of movement, and measure tile as well as body movement. Accelerometers are relatively small and inexpensive which makes them appealing to real-life applications. There are many types of accelerometer for example, piezoresistive, piezoelectric, magnetoresistive, capacitive etc in which different key technologies are used to measure acceleration [22]. Conceptually, a variation of the spring mass system is used. In this system, when acceleration is applied, a small mass inside the accelerometer responds by applying force to the spring, causing it to yield or compress. Measurement of the displacement of the spring is used to calculate the applied acceleration. Examples of accelerometer
sensor in smart home appliances are such as fall detection, activity monitoring system, etc.