As school project, and not intending to actually ever do anyone any good, you might be appropriately challenged to
- determine that it was time to sanitize
- light up an LED that was representing some sanitizing ray or light or whatever
You might program a duration for the rays and provide means to protect humans from exposure.
Do you think this would satisfy the teacher?
Detecting a package present
broken light beam (photocell detector)
weight on a platform (load cell or weight sensitive switch)
The rest is just code. Is programming part of your studies or something you are starting from scratch on your own?
It is a relatively easy program once you have the detection part, if is not something you are being taught it may be possible for you to learn just enough to hack your way through this by watching a tutorial series on youtube or working through the simple examples offered in the IDE.