Problem: I’ve driven off after my friends have gotten stuff out of my car trunk but before they’ve closed it. Thinking about this problem, its baked into my usual wait period when dropping someone off, the weirdness of hearing the thunking of the trunk when you’re not the one opening or closing it, and the fact that its all directly behind you. Audio feedback would be a good way to help differentiate the trunk’s state when the driver is not the one operating.
Solution: More or less, different audio cues based on trunk status. Traditionally there is a slap slap slap done by someone on the side of the car that means “you’re good to drive off now,” but this could be communicated better. It is important this does not confuse the driver though, and should be noticeably distinct from any relevant “trunk open” or “door ajar” sounds that they may also be hearing during normal trunk procedures. So, the system differentiated through kinetic sound when the drunk is closed, and more electronic audio when the trunk is ajar or being fuddled with. The former is accomplished with a solenoid, and the latter, a normal speaker and ideally a weight sensor.
Proof of Concept: