Accelerometer is a transducer that is used to measure the physical or measurable acceleration experienced by an object due to inertial forces and converts the mechanical motion into an electrical output. It is defined as rate of change of velocity with respect to time

There are various kinds of accelerometers and following are few mainly used in IoT projects:

Hall-effect accelerometers: Hall-effect accelerometers are using Hall principle to measure the acceleration, it measures the voltage variations caused by changes in a magnetic field around them.

Capacitive accelerometers: Capacitive accelerometers sensing output voltage dependents on the distance between two planar surfaces. Capacitive accelerometers are also less prone to noise and variation with temperature.

Piezoelectric accelerometers: Piezoelectric sensing principle is working on the piezoelectric effect. Piezo-film based accelerometers are best used to measure vibration, shock, and pressure.

Gyroscope sensors

A sensor or device which is used to measure the angular rate or angular velocity is known as Gyro sensors, Angular velocity is simply defined as a measurement of speed of rotation around an axis. It is a device used primarily for navigation and measurement of angular and rotational velocity in 3-axis directions. The most important application is monitoring the orientation of an object.

Humidity sensors

Humidity is defined as the amount of water vapour in an atmosphere of air or other gases. The most commonly used terms are “Relative Humidity (RH)

Following are key type of optical sensors:

Photodetector: It uses light sensitive semiconductor materials like photocells,photodiodes or phototransistors to work as photodetector

Fiber Optics: Fibers optics carry no current, So its immune to electrical & electromagnetics interference and even in damaged condition no sparking or shock hazard happens.

Pyrometer: It estimates the temperature of an object by sensing the color of the light and Objects radiate light according to their temperature and produce same colors at same temperature.

Proximity & Infrared: Proximity use light to sense objects nearby and Infrared are used where visible light would be inconvenient.

Acoustic, sound, vibration

Geophone

Hydrophone

Lace Sensor a guitar pickup

Microphone

Seismometer

Sound locator

Automotive

Air flow meter

Air–fuel ratio meter

AFR sensor

Blind spot monitor

Crankshaft position sensor

Engine coolant temperature sensor

Hall effect sensor

Wheel speed sensor

Airbag sensors

Automatic transmission speed sensor

Brake fluid pressure sensor

Camshaft position sensor

Cylinder Head Temperature gauge

Crankshaft position sensor

Engine crankcase pressure sensor

Exhaust gas temperature sensor

Fuel level sensor

Fuel pressure sensor

Knock sensor

Light sensor

MAP sensor

Mass airflow sensor

Oil level sensor

Oil pressure sensor

Oxygen sensor (O2)

Parking sensor

Radar sensor

Speed sensor

Throttle position sensor

Tire pressure sensor

Torque sensor

Transmission fluid temperature sensor

Turbine speed sensor

Variable reluctance sensor

Vehicle speed sensor

Water-in-fuel sensor

Wheel speed sensor

ABS Sensors

Chemical

Breathalyzer

Carbon dioxide sensor

Carbon monoxide detector

Catalytic bead sensor

Chemical field-effect transistor

Chemiresistor

Electrochemical gas sensor

Electronic nose

Electrolyte–insulator–semiconductor sensor

Energy-dispersive X-ray spectroscopy

Fluorescent chloride sensors

Holographic sensor

Hydrocarbon dew point analyzer

Hydrogen sensor

Hydrogen sulfide sensor

Infrared point sensor

Ion-selective electrode

Nondispersive infrared sensor

Microwave chemistry sensor

Nitrogen oxide sensor

Olfactometer

Optode

Oxygen sensor

Ozone monitor

Pellistor

pH glass electrode

Potentiometric sensor

Redox electrode

Smoke detector

Zinc oxide nanorod sensor

Electric current, electric potential, magnetic, radio

Current sensor

Daly detector

Electroscope

Electron multiplier

Faraday cup

Galvanometer

Hall effect sensor

Hall probe

Magnetic anomaly detector

Magnetometer

Magnetoresistance

MEMS magnetic field sensor

Metal detector

Planar Hall sensor

Radio direction finder

Voltage detector

Environment, weather, moisture, humidity

Actinometer

Air pollution sensor

Bedwetting alarm

Ceilometer

Dew warning

Electrochemical gas sensor

Fish counter

Frequency domain sensor

Gas detector

Hook gauge evaporimeter

Humistor

Hygrometer

Leaf sensor

Lysimeter

Pyranometer

Pyrgeometer

Psychrometer

Rain gauge

Rain sensor

Seismometer

SNOTEL

Snow gauge

Soil moisture sensor

Stream gauge

Tide gauge

Flow, fluid velocity

Air flow meter

Anemometer

Flow sensor

Gas meter

Mass flow sensor

Water meter

Ionizing radiation, subatomic particles

Cloud chamber

Geiger counter

Geiger–Müller tube

Ionization chamber

Gaseous ionization detectors

Neutron detection

Proportional counter

Scintillation counter

Semiconductor detector

Thermoluminescent dosimeter

Navigation instruments

Airspeed indicator

Altimeter

Attitude indicator

Depth gauge

Fluxgate compass

Gyroscope

Inertial navigation system

Inertial reference unit

Magnetic compass

MHD sensor

Ring laser gyroscope

Turn coordinator

Variometer

Vibrating structure gyroscope

Yaw-rate sensor

Position, angle, displacement, distance, speed, acceleration

Auxanometer

Capacitive displacement sensor

Capacitive sensing

Flex sensor

Free fall sensor

Gravimeter

Gyroscopic sensor

Impact sensor

Inclinometer

Incremental encoder

Integrated circuit piezoelectric sensor

Laser rangefinder

Laser surface velocimeter

LIDAR

Linear encoder

Linear variable differential transformer (LVDT)

Liquid capacitive inclinometers

Odometer

Photoelectric sensor

Piezoelectric accelerometer

Position sensor

Position sensitive device

Angular rate sensor

Rotary encoder

Rotary variable differential transformer

Selsyn

Shock detector

Shock data logger

Tilt sensor

Tachometer

Ultrasonic thickness gauge

Ultra-wideband radar

Variable reluctance sensor

Velocity receiver

Optical, light, imaging, photon

Charge-coupled device

CMOS sensor

Colorimeter

Contact image sensor

Electro-optical sensor

Flame detector

Infra-red sensor

Kinetic inductance detector

LED as light sensor

Light-addressable potentiometric sensor

Nichols radiometer

Fiber optic sensors

Optical position sensor

Thermopile laser sensors

Photodetector

Photodiode

Photomultiplier tubes

Phototransistor

Photoelectric sensor

Photoionization detector

Photomultiplier

Photoresistor

Photoswitch

Phototube

Scintillometer

Shack–Hartmann wavefront sensor

Single-photon avalanche diode

Superconducting nanowire single-photon detector

Transition-edge sensor

Visible-light photon counter

Wavefront sensor

Pressure

Barograph

Barometer

Boost gauge

Bourdon gauge

Hot filament ionization gauge

Ionization gauge

McLeod gauge

Oscillating U-tube

Permanent downhole gauge

Piezometer

Pirani gauge

Pressure sensor

Pressure gauge

Tactile sensor

Time pressure gauge

Force, density, level

Bhangmeter

Hydrometer

Force gauge and Force Sensor

Level sensor

Load cell

Magnetic level gauge

Nuclear density gauge

Piezocapacitive pressure sensor

Piezoelectric sensor

Strain gauge

Torque sensor

Viscometer

Thermal, heat, temperature

Bolometer

Bimetallic strip

Calorimeter

Exhaust gas temperature gauge

Flame detection

Gardon gauge

Golay cell

Heat flux sensor

Infrared thermometer

Microbolometer

Microwave radiometer

Net radiometer

Quartz thermometer

Resistance thermometer

Silicon bandgap temperature sensor

Special sensor microwave/imager

Temperature gauge

Thermistor

Thermocouple

Thermometer

Pyrometer

Proximity, presence

Alarm sensor

Doppler radar

Motion detector

Occupancy sensor

Proximity sensor

Passive infrared sensor

Reed switch

Stud finder

Triangulation sensor

Touch switch

Wired glove

Sensor technology

Active pixel sensor

Back-illuminated sensor

Biochip

Biosensor

Capacitance probe

Capacitance sensor

Catadioptric sensor

Carbon paste electrode

Digital sensors

Displacement receiver

Electromechanical film

Electro-optical sensor

Electrochemical fatigue crack sensor

Fabry–Pérot interferometer

Fisheries acoustics

Image sensor

Image sensor format

Inductive sensor

Intelligent sensor

Lab-on-a-chip

Leaf sensor

Machine vision

Microelectromechanical systems

Photoelasticity

Quantum sensor

Radar

Ground-penetrating radar

Synthetic aperture radar

Radar tracker

Stretch sensor

Sensor array

Sensor fusion

Sensor grid

Sensor node

Soft sensor

Sonar

Staring array

Transducer

Ultrasonic sensor

Video sensor

Visual sensor network

Wheatstone bridge

Wireless sensor network

Speed sensor

Speed sensors are machines used to detect the speed of an object, usually a transport vehicle. They include:

Wheel speed sensors

Speedometers

Pitometer logs

Pitot tubes

Airspeed indicators

Piezo sensors (e.g. in a road surface)

LIDAR

Ground speed radar

Doppler radar

ANPR (where vehicles are timed over a fixed distance)

Laser surface velocimeters for moving surfaces