HS design project

My son has to build a project for his science class that is “useful “. It can be anything as long as it is original. He wants to build a device that can be put on the mailbox so that when the mailman opens the box, a switch is triggered that sends a message to his phone telling him that he’s got mail. How hard is this to do? Can anyone give me some advice on what would be required and where to buy it? I was hoping to get an existing device like a “Ring” doorbell and rig it so it calls the phone when the mailbox opens. Basically,I’m a mom with very little electronics xp that wants to help her son pass his class. Any suggestions??

It can be done with no electronics knowledge.
Set up an old phone so that when you press a button it sends a text, and arrange a linkage of somekind so that the flag on the mailbox presses said button.
Or if you dont mind hacking the phone connect an external switch to the button with a pair of wires.
Another way to do it would be to use something like an arduino or esp8266, but that gets very complex, still do able but you'd have to learn quite a bit.