PIR sensors are used to detect motion from pets/humans from about 20 feet away (possibly works on zombies, not guaranteed). This one has an adjustable delay before firing (approx. 2-4 seconds), adjustable sensitivity and we include a 1 foot (30 cm) cable with a socket so you can easily reposition the sensor or mount it using the two drills on either side.
Reed switch is a kind of passive electronic switching component with contacts with a simple structure, small size and easy to control. It consists of a sealed glass envelope where there are two ferrous elastic reeds and is filled with inert gas.