Wearable devices use all kinds of sensors, depending on the application. Manufacturers worldwide produce sensors because they are an essential part of all wearable devices. Therefore, in this article, we review sensor characteristics by dividing them into four main groups: environmental sensors, biosensors, location tracking sensors, and other sensors.
Environmental sensors
Sensors are used to measure, monitor, and record environmental conditions or properties like barometric pressure, relative humidity, luminosity, temperature, dust, and water level. In scientific applications and daily consumer products such as motion light sensors, ambient light sensors, external lights, safety lights, and traffic light sensors, light sensors are widely used for light detection. To determine an environment’s sound intensity, use sound sensors or microphones. They come in multiple forms, including dynamic condensers, ribbons, carbon, and microphones. The most common type is dynamic microphones measuring noise levels in decibels at human-sensitive frequencies.
For humidity and temperature measurements, a humidity sensor measures the relative humidity in the air. These are sometimes referred to as humidity/dew sensors and can be found in heating, ventilation, or air conditioning systems. For detecting open flames or fire, flame sensors are more sensitive and accurate than commonly used smoke or heat detectors. Smoke, alcohol, and other harmful airborne gases perform a similar function.
Biosensors
Biosensor scope has increased with increasing health surveillance demand. These sensors allow people always to be aware of their condition and are used by health professionals for early diagnosis and disease prevention. Examples include sensors for body temperature, heart, and heart monitoring, electrocardiogram (ECG), electroencephalography, electromyography (EMG).
To measure the electrical activity of the heart, a heart rate monitoring module can be used to extract, amplify, or filter bio-potential signals to create heart rate. Usually, biomedical sensor pads and cables are required for heart monitoring. The cardiac finger clip sensor is a high-performance optical biosensor that measures body blood changes. In medical electronics, biosensors are everyday indoor use to monitor patient health.
Position and location tracking sensors
The most common types of sensors on wearable devices, such as activity trackers, smartwatches, and even medical wearables, are location and position tracking sensors (i.e., GPS, altimeters, compasses, and accelerometers). Used for physical and health checks. A GPS module is a three-axis sensor used to determine location, altitude, and speed at any time in most weather conditions. However, there are few examples of using GPS modules (for tracking purposes only in open-pit mines). Since no indoor signals are required for GPS modules, they are considered inappropriate for underground tracking systems. A compass is a simple magnetometer defining magnetic climate field direction.
Use a magnetometer sensor to measure the magnetic field at a specific location. It can be used to track metallic vehicles and human body movements (used together with an accelerometer and/or smartphones), as it can detect iron metals. The accelerometer with expanded sensing capability is another common inertial sensor type. Available in one, two, three, or six-axis applications, they have a high capacity for fall detection and safety management.
Other sensors
Various other detectors and sensors are also available on the market, usually on consumer wearable devices. Wearable cameras and smart glasses are often described as the central part along with camera sensors. Communication sensor modules (Bluetooth, RFID, Wi-Fi, etc.) provide communications and data interactions for wearable devices. These sensors are used for monitoring purposes. Also used as motion sensors, velocity sensors, inert unit (IMU) (accelerometer compound unit, gyroscope and sometimes magnetometers), ultrasonic sensors and IR sensors (small photocell photo chips with infrared light captured).
