This is a very small light sensor. A photo resistor (also known as a photodector, or photocell) changes resistance depending on the amount of light it is exposed to.
The HC-SR501 is a passive infro-red (PIR) sensor which is used to detect motion based on the infrared heat in the surrounding area.
The H8054 PIR motion detection module provides basic motion detection in a small package. Compatible with the Arduino and Raspberry Pi
The HD2 tracked platform is a large, heavy duty tracked robot with the power to pull a truck and climb stairs. A wealth of internal space allows for batteries, controls and an optional computer.