If you have a garden that is constantly being eaten by deer, rabbits, or whatever it may be, this will scare them away. A trip wire that sets off a small fire.

This website gives a deeper explanation: https://interestingengineering.com/create-trip-wire-alarm-simple-items

Here is how you make it:

This directly relates to engineering because it uses a multi-stage system to set off a reaction. You have to create the system or in other words, engineer the system, in order for it to work.