An indicator to see if you have received anything in your mailbox. A magnet in the mailbox lid holds the indicator in place, when the lid is opened the indicator falls down. See it in action in this video: https://youtu.be/8i_Zg3tA40A

You will need a few small things for this to work:

• Glue
• A washer not more than 16 mm in diameter and no more than 1.75mm thick (you should also check to see if it will stick to a magnet)
• A small magnet
• Double-sided tape