I would like to attach a sensor to the bottom of my letterbox so that when a parcel or a letter is dropped in it I would receive instant notification. Ideally the sensor would be able to be configured to certain impact threshold and to report the value.
What kind of sensor could I use for that purpose? What kind of device could it be connected to which would be able to trigger a network event (e.g. HTTP request)?
The letterbox is this one (not my photo):