Our house is pretty far away from our mailbox, and we need to walk uphill to go check the mail. The mailman has very variable hours, so we often find ourselves going 3-4 times to the mailbox during the day. My dad is an avid DIYer, and has given himself a challenge: find a way to know when the mailman drops mail in our mailbox. He has thought about a lot of different solutions and none really fit our use case. We looked up online for other people who have done that, but every one seems to use WIFI. Our WIFI unfortunately doesn't reach that far, as the mailbox is quite distant from the house (we measured 50 meters / 164 feet).
He first thought about putting a WIFI camera in the mailbox. However, WIFI doesn't reach that far (the router is in his office, I put it on the diagram).
He also thought about running a cable from the house to the mailbox, attached to a sensor or a camera. However, a part of the path is made out of concrete, and burying the cable would be super hard. He could also run it through the garage, there is a little space between the roof and walls so a cable would probably fit. However, he would then have to drill through the house's walls and having done it in the past, it is a real pain.
He thought about buying a camera or sensor that uses a SIM card to connect to a network that will be picked up by his phone. However, our country forbids the use of SIM cards for communication that is not person-to-person. He would have to get a more expensive kind of card.
He thought about putting a WIFI repeater in the garage, but finds this solution a bit overkill and expensive.
This is a diagram I made of our house configuration using a map:
We are looking for a solution that is not too expensive and doesn't involve a lot of wall drilling. I have read about people using radio sensors (for instance a tilt sensor on the letterbox door), but knowing nothing about radio waves, we are a bit lost.
What would be an ideal solution to remotely check if the mailman has dropped mail today?