I had exactly the same problem. First I fixed a big arrow to the box, which the postie flicked the opposite way when putting stuff in the box. That meant I could see it from just outside the house, from a distance - no need to go to the box.

Then, I bought a remote bellpush which is now fixed, under a waterproof cover, to the box. The sounding part is plugged into a mains socket inside the house. The two are a fair distance from each oter, maybe 150m, and it works well. All I have to do now is train the postie to press it every time a letter arrives, not just when there's a parcel. Catching him is proving difficult. I'm looking for a more automatic method - maybe a spring connected to the flap that presses the doorpush as the flap is opened?

I had exactly the same problem. First I fixed a big arrow to the box, which the postie flicked the opposite way when putting stuff in the box. That meant I could see it from just outside the house, from a distance - no need to go to the box.

Then, I bought a remote bellpush which is now fixed, under a waterproof cover, to the box. The sounding part is plugged into a mains socket inside the house. The two are a fair distance from each other, maybe 180', and it works well. All I have to do now is train the postie to press it every time a letter arrives, not just when there's a parcel. Catching him is proving difficult. I'm looking for a more automatic method - maybe a spring connected to the flap that presses the doorpush as the flap is opened?