What is sensor ( Detector ) ?

A sensor is a device that detects and responds to some type of input from the physical environment. The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal that is converted to human-readable display at the sensor location or transmitted electronically over a network for reading or further processing. 

Motion sensors in various systems including home security lights, automatic doors and bathroom fixtures typically send out some type of energy, such as microwaves, ultrasonic waves or light beams and detect when the flow of energy is interrupted by something entering its path. 

A photosensor detects the presence of visible light, infrared transmission (IR), and/or ultraviolet (UV) energy.

Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base, besides innumerable applications of which most people are never aware. With advances in micro machinery and easy-to-use micro controller platforms, the uses of sensors have expanded beyond the more traditional fields of temperature, pressure or flow measurement,[1] for example into MARG sensors. Moreover, analog sensors such as potentiometers and force-sensing resistors are still widely used. Applications include manufacturing and machinery, airplanes and aerospace, cars, medicine and robotics.

Photo Sensors
-Amplifier built-in photo sensor
-Fiber sensor
-Laser sensor
-Free power source photo sensor
-U-shaped photo sensor
-Distance settable sensor
-Scanning range finder
-Distance sensor
-Displacement sensor
-Sensors for special applications
-Microwave sensor
-Ultrasonic sensor
Miniature Photoelectric Sensors
Special Purpose Photoelectric Sensors
Clear Object Sensors
-Communication Sensor
-Label Sensor
-Contents Detection
Registration Mark Sensors