The function of a sensor is to receive some action from a single phenomenon of the subject of measurement and to convert this to another physical phenomenon that can be more easily handled.

Many early sensors converted a physical measured to mechanical energy; for example, pneumatic energy was used for fluid controls and mechanical energy for kinematic controls. However, the introduction of solid-state electronics created new opportunities for sensor development and control, with the resultant that sensors today almost exclusively produce an electrical output for use in such applications as computer-based controls, archiving/recording, and visual display. This need for electrical interfacing is causing a broadening in the definition of a sensor to include the systems interface and signal conditioning features that from an integral part of the sensing system.

CONVERTING ENERGY

Mechanical	length, area, volume, time derivatives such as velocity and acceleration, mass flow, force, torque, pressure, acoustic wavelength and intensity
Thermal	temperature, specific heat, heat flow, state of matter
Electrical	voltage, current, charge, resistance, inductance, capacitance, dielectric constant, polarization, electric field, frequency, dipole moment,
Magnetic	field intensity, flux density, magnetic moment, permeability,
Radiant	intensity, phase, wavelength, polarization, reflectance, transmitance, refractive index,
Chemical	composition, concentration, reaction rate, pH, oxidation/reduction potential, gas, odor, ions
Biological	touch, vision, smell

There is a clear trend towards device miniaturization and distributed 'intelligent' instrumentation. Researchers are concerned with sensor design for manufacturability, and for improvement of actuation to implement control action within use systems.

In intelligent buildings already existing now, particularly in high-rise building, are founded in part on building automation. The aim is to benefit both residents and building mangers by optimizing environmental and safety aspects in an economical way. This is achieved by using computers together with function distribution control techniques to optimize the running of the various pieces of equipment within the building. Such examples are air conditioning, fire-prevention and security devices that effectively use the sensory system.

Examples of sensors:

Photo-detection	Quantum detectors - convert incoming radiation directly into an electron in semi-conductor device and process the resulting current.
Thermal detector	absorb the energy and simply measure the change of thermal energy with a thermometer.
Motion sensor	Movement of an object within the monitored region causes a change in light levels at one or both photoresistors. The changes in resistance are used to create an output signal.
Infrared Detection	Common for reading room temperature bodies are thermal detectors which operate by absorbing the infrared radiation and measuring the temperature rise of the detector with a thermometer.

Biosensors	The sensing element that responds to the substance being measured is biological in nature. Biosensors are generally concerned with sensing and measuring particular chemicals that need not be biological components themselves.
Photoresistor	Light-sensitive resistor whose resistance changes with light.
Photodiode	Light-sensitive diode that produces a current in response to light
Phototransistor	Designed to be sensitive to light. Detects fluctuating light signals.
Thermistor	Temperature-sensitive resistor whose resistance changes with temperature
Microphone	Sound-sensitive sensor that produces a voltage or changes a capacitance as the sound level changes.

Upon thinking of applying new technology of sensor to the homes of the future, smart structure can lead one to mesh the structure of the building and sensor together. Sensors are one of the essential components of a smart structure. (Smart structure: a system that keeps structure in a certain state or the structure reacts according to a set of rules. The system of sensors and actuators together with control system comprises the structure.) Sensors will provide the ability to monitor and measure external stimuli to subsequent behavior throughout the structural medium. Examples of such sensors in the process of development are the following:

Acoustic sensors	very perceptive systems but problems are resulting from the character of the wavelengths and the elimination of interfering signals generated in stressed materials have not been overcome yet.
Microelectronic sensors	that has advantages in their variability and the possibility of data preprocessing. Considerable effort has been focused on the interconnection of sensors into network where qualitative advances in the transmission of electronic signals are expected. If the induced breakdowns of signals that are processed at low frequencies were eliminated, then microelectronic sensors would have a higher profile.
Piezo-electric sensors	this is based on piezo-electric phenomenon. Various crystals or ceramics that produce a voltage when bent, vibrated or subjected to mechanical shock.
Optical fibers	it enables the detection of the whole range of physical parameters such as: temperature, deformation, electrical and magnetic fields, changes in chemical composition without destruction of the observed material. By using various types of modulation (intensity, phase, polarizing or inter mode modulation) as significant resistance of the sensor system to breakdown or disturbing fields can be achieved. Fiberoptics sensors are used in monitoring civil engineering structures. They are embedded into the composite structures providing a 'sensor skin' that can sense the impact damage to the aircraft. When a strand of fiber breaks, the light signal being fed through the fiber to a sensor is interrupted, indicating a potential failure.