Sensors are devices that respond to signals or stimuli from an output. There are several types of sensors, such as infrared, which interact with infrared energy, or heat that can’t be physically seen. The output of the sensor depends on the type of device, such as opening a door, dispensing soap, or turning the lights on. Below are two images, one of a sensor and the other a chart of ultraviolet and infrared energy and wavelength.
Below are two more images of infrared sensors, one with the light on, and the other with the light off, due to the hand hovering over the sensor.
While an impressive piece of technology, there are some drawbacks to sensors, mostly cheap sensors, such as having difficulties differentiating heat signatures, due to lack of strength when scanning for infrared radiation. In other words, companies cheap out and use cheaper sensors for their products. Of course, the sensors themselves should not be blamed for their flaws, rather, the manufacturers behind these devices should be responsible for the implementation of cheap sensors in their products. These types of sensors are not properly designed to catch bugs, and are not programmed in a way to tackle certain conditions, rendering them as unreliable.