Is This Gadget Real or Just a Concept?

Hailing from Japan, the Thanko Mailbox Sentry is a device that notifies you when you receive snail mail. A sensor is attached to the inside of your mailbox, and when the box is stuffed with actual mail, it sends a signal to a handset inside your home. If you're waiting for something important, this gadget would certainly cut down the amount of time you spend trudging back and forth to the mailbox, but is it real?