6.10. Accelerometer.
An accelerometer is an electronic tool
that measures acceleration forces accurately. In SHSs, ac-
celerometers are used to detect the acceleration of a person
who is static or dynamic [23], identify intrusion [68], and
detect the mobility and condition of a patient in a smart
home [13, 106].
6.11. Door Sensor.
A door sensor is a device that detects
a door opening or closing and notifes the user. A pair of
electrical connectors detects the opening or closing by
making or breaking an electrical circuit in the sensor. Tese
sensors are being used increasingly in SHSs for detecting
door opening and closing status in elderly care systems
[23, 102] and overall home occupant activity monitoring.
6.12. Gyroscope.
A gyroscope or angular velocity sensor is
a device that can measure and maintain the orientation and
angular velocity of an object. In SHSs, it is used for detecting
the orientation of a person [23], along with an accelerom-
eter, and in gesture control systems, it is used for detecting
gestures [107, 108].
6.13. Pulse Sensor.
A pulse sensor is a device that is capable
of detecting and monitoring human heart rate continuously.
In smart homes, it is mainly used for elderly health care
[23, 78].
6.14. Fluid/Water Detection Sensor.
A fuid detection sensor,
sometimes known as a raindrop sensor, is an electronic
device that can detect water via an extended pad that can
sense water on its surface. It is usually used to detect water
leakage and water level monitoring [65, 95, 100].
6.15. Camera.
Te application of a camera or a network of
cameras is becoming more and more popular in SHS de-
signs. SHS researchers have used the camera with various
computational methods such as image processing, machine
learning, gesture recognition, and artifcial intelligence for
enhancing
smart
home
security
and
monitoring
[29, 52, 109], object detection [47], gesture detection [60],
and live feed monitoring [72]. Cameras provide a reliable
method of setting up security for smart home users. Te only
drawback to using a camera is its cost of deployment and
maintenance.
6.16. Force-Sensing Resistor.
A force-sensing resistor (FSR) is
an electronic device that is capable of measuring the amount
of force, pressure, or mechanical stress applied to it. FSRs use
a type of material that changes its resistance when force is
applied to it. Tese are special types of sensors used in SHSs
to detect the home occupant’s activity [103] and set up
special systems for elderly people’s care [110].
6.17. Flex Sensor.
A fex sensor is used to measure the
amount of defection or bending of certain objects. Te
sensor works by changing the resistance when bent. Te fex
sensor is usually used in gesture-controlled systems to detect
gestures [32, 111].
6.18. Other Types of Sensors.
Aside from the types of sensors
mentioned previously, a few other types of sensors com-
bining several other sensors, such as bed sensors [71], chair
sensors, and posture sensors, have been demonstrated. Tese
sensors cannot be categorized as a single type of sensor as
they often have multiple other sensors such as motion,
accelerometer, and gyroscope sensors inside them.
6.19. Classifcation of Reviewed SHSs According to Sensors.
A summary of the various types of sensors used by the
authors for developing SHSs is provided in Table 4.