## 4 Sensors in Smart Home
### Wearable Sensors  
Wearable sensors aim to measure the motion characteristics, location, pulse rate, body temperature, blood pressure, and other vital signs of users. These sensors are usually attached to a person directly (e.g., bracelet sensors or cardio sensors) or attach to their clothes (e.g., an accelerometer or a step counter). Table 4 is a summary of wearable sensors that are used for activity recognition and activities of daily living (ADL) classification.  
* Accelerometers--Accelerometers are the most popular sensors for movement and activity recognition [35; 36]. These sensors usually attached to a specified part of the human body. Location accelerometers are able to distinguish various types of movement (e.g., running, walking, sitting, scrubbing, etc.) [37; 38] or assist to figure out the user posture [39]. Sometimes, accelerometers are employed to detect falls by measuring acceleration [40]. To improve the accelerometers performance and enrich the collected information, accelerometers are often employed together with gyroscopes [41].
* Hand-worn sensors--These sensors are widely used in several activity recognitions. Wristwatches, magnetic sensors, and other types of bracelets are classified into this group. To improve the wristwatch ability in hand gesture recognition, accelerometers are integrated to wristwatches [42]. [PERSON] et al. [43] employed a wrist-worn activity detector to classify users' sleep/awake activities. [PERSON] et al. [44] combined inertial sensors, accelerometers, and tilt switches in a wrist-worn sensor to recognize the daily activities of the user. Since different electrical devices emit different magnetic fields, hand-worn magnetic sensors which have the capability to distinguish differences among magnetic fields are employed to recognize the activity of a user [45]. Usually emergency buttons are designed for wristwatch, which can be used to ask for help [46].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sensor** & **Detected Parameter** & **Usage Example** \\ \hline Accelerometer & Movement & Occupant running and falling \\ \hline Hand-worn sensors & Gestures and step counter & Drinking, walking \\ \hline Smartphone & Movement & User sleep or activity duration \\ \hline RFID & Object-interaction & Using utensils \\ \hline Vital monitoring sensors & Vital signs & Blood pressure, heart bit rate \\ \hline \hline \end{tabular}
\end{table}
Table 4: Wearable sensors used for activity classification.  
* Smartphones--Various ranges of sensors such as accelerometers, gyroscopes, a global positioning system, a magnetometer, and a microphone integrated in smartphones. These sensors provide rich information about the user's movement and activities [47; 48].
* RFID tags--These types of sensors are mostly used for finding the interaction of occupants with particular objects and for detecting the cooking, eating, and drinking within the home, [PERSON] et al. [49] attached RFID tags on various kitchen utensils such as cutlery and dishes. Similar setups are also considered in [50; 51; 52]. RFID tags are used for dressing failures detection by [PERSON] et al. [53]. Often, RFID sensors are used in combination with other sensors such as accelerometers [54].  
In addition to these sensors, there is also a large variety of sensors that monitor persons' vital signs [33]. These sensors allow for the monitoring of a large set of human vital signs, anomaly detection, and supporting activity recognition and classification.