How to dectect presence/absence of something

Is it possible to use Arduino to detect the presence/absence of stuff, human, animal, or something else? and how to do it?

Answer

Yes, there are many ways to detect presence/absence. The choice depends on the specific application. The belows show some ways to do it.

Using the force sensor
Using the IR beam sensor
Using the reed switch
Using the GPS module
Using the accelerometer and gyroscope sensor
Using the PIR motion sensor

Using the force sensor

Object sits on the force sensor
Sensor does not need to be attached on object.
Detection bases on the weight
Example use cases: detecting something is taken away

Using the IR beam sensor

Object is placed between IR beam emitter and receiver
Sensor does not need to be attached on object.
Can detect any object
Example use cases: detecting something is taken away, intruder detection

Using the reed switch

One of two part of reed switch need to be attached on object.
Can detect any object
Example use cases: detecting something is taken away, detecting door closing/openning

Using the GPS module

Sensor need to be attached on object.
Detection bases on the position
Example use cases: bike sharing economy

Using the accelerometer and gyroscope sensor

Sensor need to be attached on object.
Detection bases on the movement
Example use cases: detecting something is taken away

Using the PIR motion sensor

Sensor does not need to be attached on human/animal
Can detect human/animal
Cannot detect if human/animal is not moving
Cannot detect object
Cannot distinguish between human/animal
Example use cases: auto lighting system, auto escalator, intruder detection

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