A passive infrared sensor (PIR sensor) is an electronic sensor that detects infrared radiation emitted from warm objects and can be used in motion detectors. It works passively by detecting infrared radiation without emitting any energy itself. Soil moisture sensors indirectly measure the volume of water in soil through properties like electrical resistance or interaction with neutrons. A photoresistor is a light-controlled variable resistor whose resistance decreases with increasing light intensity, allowing it to be used in light-sensitive detector circuits.

3. sensor is an object whose
purpose is to detect events or
changes in its environment, and
then provide a corresponding
output.
A sensor is a type of
transducer; sensors may
provide various types of
output, but typically use
electrical

6. o A passive infrared sensor (PIR
sensor) is an electronic sensor that
measures infrared (IR) light
radiating from objects in its field of
view. They are most often used in
PIR-based motion detectors.
o All objects with a temperature above absolute zero emit heat
energy in the form of radiation. Usually this radiation isn't visible to
the human eye because it radiates at infrared wavelengths, but it
can be detected by electronic devices designed for such a purpose.

7. o The term passive in this instance refers to the fact that PIR devices do not
generate or radiate any energy for detection purposes. They work entirely by
detecting the energy given off by other objects. PIR sensors don't detect or
measure "heat"; instead they detect the infrared radiation emitted or
reflected from an object.
A motion detector attached to
an outdoor, automatic light.

8. Soil moisture sensors measure the volumetric water content in
soil. Since the direct gravimetric measurement of free soil moisture
requires removing, drying, and weighting of a sample, soil moisture
sensors measure the volumetric water content indirectly by using
some other property of the soil, such as electrical resistance,
dielectric constant, or interaction with neutrons, as a proxy for the
moisture content.

9.  A photoresistor (or light-dependent
resistor, LDR, or photocell) is a light-
controlled variable resistor. The resistance
of a photoresistor decreases with increasing
incident light intensity in other words, it
exhibits photoconductivity. A photoresistor
can be applied in light-sensitive detector
circuits, and light- and dark-activated
switching circuits.
LDR

11. These sensors translate
the temperature into a
reference voltage,
resistance or current,
which is then measured
and processed and a
numerical temperature
value is generated.