Very probably not. I have mounted an Aqara vibration sensor in the letterbox as a test; it should be comparably strong. As the crow flies, the distance to the next active node on the first floor is about 10m. In between is the letterbox itself, which is made of metal, a glass window behind the letterbox, the staircase and then the wall of the flat and a bit of ceiling and plastic because the receiver node is in a flush-mounted shaft. No connection. Maybe it would work if there was another node as close as possible to the outside wall, such as an Ikea Tradfri adapter plug. This could then transmit the signal.