German company offers a very cool gadget called POSTIN. The device notifies owners when the mailman is dropping mail in the mailbox. This is a genius gadget for people like me who live in the 4th floor.

The POSTIN device uses a radio signal that works depending on the building or landscape over a 50 to 250m distance. In buildings it should reach up to the 7th floor. It uses automatic changing signature codes to not interfere with other POSTIN devices in the vicinity.
The sender needs to be attached to the latch of the mailbox (see photo below). When it is dropped a sensor is triggered and a signal is sent to the receiver unit. The receiver has a time display that starts flashing when it has received the signal that there is new mail in the mailbox. An audio signal can also be enabled on the receiver.
The gadget sells for 69 Euros online in Germany. This gadget could also be a big hit in the USA, where every unnecessary footstep is to be avoided at all costs.
More details on the POSTIN site (German) (Thanks Cerstin L.).