Every component that interacts with the physical world, is a hardware. Since IoT is a network of day to day devices and machines, sensors are to play a vital role in this technology. Not only sensors but many other hardware components are involved in an IoT architecture. Following is a list of all the major hardware components.
Accelerometer: A sensor that senses acceleration.
Magnetometer: A sensor that senses magnetic field intensity.
Gyroscopes: A sensor that senses angular motion and orientation.
Pressure Sensor: A sensor that senses pressure.
Temperature Sensor: A sensor that senses temperature.
Humidity Sensor: A sensor that senses humidity.
Proximity Sensor: A sensor that senses presence of nearby objects.
Light Sensor: A sensor that senses light.
Helmet: In order to avoid any accident, a smart Helmet can be designed using some specific sensors.
Glasses: A smart spectacle can be designed so that the user wearing that can send the live scene/footage to some one else.
Jewelry: Smart jewelries can be designed in order to sence the specific body parts.
Wristbands: Wristbands are quite a lot popular in modern fashion The sense things like pulse, oxygen level etc.
Belts: Smart belts can be designed in order to sence the organs in the torso and pelvic area.
Socks and Shoes: Smart socks and shoes can be designed in order to sence the ankle area.
Hydraulic Actuators: A machanism that can produce motion from hydraulic activities.
Pneumatic Actuators: A machanism that can produce motion from air pressure kind of activities.
Electrical Actuators: A machanism that can produce motion from electrical voltages.
Magnetic Actuators: A machanism that can produce motion from magnetic activities.
Thermal Actuators: A machanism that can produce motion from thermal activities.
Switches: A networking device that can connect many compatible devices or computers. Switches are generally used for creating a LAN with star topology.
Routers (WiFi): Another networking device to connect two or more LANs together. Generally a WiFi router (Wireless router) is used in IoT ecosystem to provide wireless connetivity among smart devices.
Internet Gateways: A device used to connect the personal WiFi router to the gigantic Internet.
IoT is coceived not only to notify a user about the real world problems and happenings, but also to let the user control those happenings. That is the reason we need actuators also in this ecosystem.