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Figure 6: Typical thermistor interface. value, based on the sensors’ material. Typically, as temperature increases, most conductors also increase their resistance, as they are usually molted by metals [29]. Platinum is the most common material used to make RTDs while thermistors are usually made from a polymer or ceramic material. In most cases, thermistors are cheaper but they are also less accurate compared to RTDs. Thermocouples are made by joining two dissimilar metal wires together; the temperature difference between them produces a measurable voltage difference that is used to calculate the temperature (Seebeck effect). Lastly, semiconductor-based temperature sensors are ICs that measure their own die temperature by using the physical properties of a transistor (or an external transistor for remote ones) (Figure 6).

Figure 6 Typical thermistor interface. value, based on the sensors’ material. Typically, as temperature increases, most conductors also increase their resistance, as they are usually molted by metals [29]. Platinum is the most common material used to make RTDs while thermistors are usually made from a polymer or ceramic material. In most cases, thermistors are cheaper but they are also less accurate compared to RTDs. Thermocouples are made by joining two dissimilar metal wires together; the temperature difference between them produces a measurable voltage difference that is used to calculate the temperature (Seebeck effect). Lastly, semiconductor-based temperature sensors are ICs that measure their own die temperature by using the physical properties of a transistor (or an external transistor for remote ones) (Figure 6).

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Figure 1: Dual-mode motion sensors [17]. There are five types of area motion detection sensors: passive infra-red, microwave, ultrasonic, radar and vibration. The first type detects body heat (infrared energy) by monitoring changes in temperatures. The second type sends out microwave pulses and measures the reflections off of moving objects. Similarly, the third type measures distance using ultrasonic sound waves (non-audible by humans) shared and received to measure objects’ proximate positions while radar types measure the reflection from a laser beam emission to the obstacles in in environment. Vibration motion sensors detect small vibrations that people cause when they move through a room; while they are small in size, they can be unreliable. None of these sensors measure motion per se. Last, dual motion sensors can combine multiple detection methods in an attempt to reduce false alarms. For example, it is not uncommon for a dual technology sensor to combine a passive infrared (PIR) sensor with a microwave sensor, each operating in a different spectrum. Nevertheless, any change in distance measurement will rigger rapid and reliable motion events [16] (Figure 1). Typical low-cost sensors used in smart home applications are HC-SR04, SEN 14588 and VL6180.
Figure 1: Dual-mode motion sensors [17]. There are five types of area motion detection sensors: passive infra-red, microwave, ultrasonic, radar and vibration. The first type detects body heat (infrared energy) by monitoring changes in temperatures. The second type sends out microwave pulses and measures the reflections off of moving objects. Similarly, the third type measures distance using ultrasonic sound waves (non-audible by humans) shared and received to measure objects’ proximate positions while radar types measure the reflection from a laser beam emission to the obstacles in in environment. Vibration motion sensors detect small vibrations that people cause when they move through a room; while they are small in size, they can be unreliable. None of these sensors measure motion per se. Last, dual motion sensors can combine multiple detection methods in an attempt to reduce false alarms. For example, it is not uncommon for a dual technology sensor to combine a passive infrared (PIR) sensor with a microwave sensor, each operating in a different spectrum. Nevertheless, any change in distance measurement will rigger rapid and reliable motion events [16] (Figure 1). Typical low-cost sensors used in smart home applications are HC-SR04, SEN 14588 and VL6180.
Besides fire smokes, gas leaks are among the main domestic dangers for residents. They constitute health hazards, especially when they are toxic and odorless. Toxic gas sensors are able to detect several gases, such as petroleum gas, smoke, alcohol, propane, hydrogen, methane and carbon monoxide. Their operation is the following: when the outer layer of a sensor is heated in high air temperatures, it absorbs oxygen from its surroundings. These sensors can determine the type of gas based on the oxygen’s density, in addition to measuring the flow of the current [20]. However, the vast majority of low-cost toxic gas sensors are unreliable. Furthermore, they cannot distinguish between different gases but rather provide a generic estimate, based on a reference gas (Figure 3).
Besides fire smokes, gas leaks are among the main domestic dangers for residents. They constitute health hazards, especially when they are toxic and odorless. Toxic gas sensors are able to detect several gases, such as petroleum gas, smoke, alcohol, propane, hydrogen, methane and carbon monoxide. Their operation is the following: when the outer layer of a sensor is heated in high air temperatures, it absorbs oxygen from its surroundings. These sensors can determine the type of gas based on the oxygen’s density, in addition to measuring the flow of the current [20]. However, the vast majority of low-cost toxic gas sensors are unreliable. Furthermore, they cannot distinguish between different gases but rather provide a generic estimate, based on a reference gas (Figure 3).
Figure 2: Flame detector type regions. While responses to a detected flame depend on the installation, they can include sounding an alarm, deactivating a fuel line (such as a propane or a natural gas line), and activating a fire suppression system (Figure 2). EO Typical low-cost sensors used in smart home applications are RE46C190 and YG1006.
Figure 2: Flame detector type regions. While responses to a detected flame depend on the installation, they can include sounding an alarm, deactivating a fuel line (such as a propane or a natural gas line), and activating a fire suppression system (Figure 2). EO Typical low-cost sensors used in smart home applications are RE46C190 and YG1006.
Figure o: mau oifect principles | 20}. Typical low-cost sensory solutions used in smart homes applications regarding magnetic fields are 2SS52M and SS49E. The Hall effect provides information regarding the type of magnetic pole and magnitude of the magnetic field. For example, a south pole would cause the device to produce a voltage output while a north pole would have no effect. Generally, Hall Effect sensors and switches are designed to be in “OFF’, (open circuit condition) when there is no magnetic field present. They only turn to “ON’, (closed circuit condition) when subjected to a magnetic field of sufficient strength and polarity (Figure 5).
Figure o: mau oifect principles | 20}. Typical low-cost sensory solutions used in smart homes applications regarding magnetic fields are 2SS52M and SS49E. The Hall effect provides information regarding the type of magnetic pole and magnitude of the magnetic field. For example, a south pole would cause the device to produce a voltage output while a north pole would have no effect. Generally, Hall Effect sensors and switches are designed to be in “OFF’, (open circuit condition) when there is no magnetic field present. They only turn to “ON’, (closed circuit condition) when subjected to a magnetic field of sufficient strength and polarity (Figure 5).
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Remote SensingSensors and SensingSmart SensorsSmart HomeSmart HomesWireless Sensor Networks (WSNs)Smart houseSmart HousesInternet of Things (IoTs)Sensor Networks and IoT
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