The link between smells and memory is poorly understood and very strong. While sounds, images, even touches can evoke memories, we've all experienced that moment when a smell we couldn't even describe (there are so few words to describe smells) immediately brings out a memory from long ago, with more force than any of the other stimuli. It's probably some vestige of our ancestry in animals that used scent more the other senses to make a living; we've adapted to use more of our brains for vision than smell, and our smell has withered away to a barely-working organ compared to other animals, but there's still some potent linking mechanism in our brains still firing.
No one really knows why some smells have so much power to evoke a memory and others not that much. But I wonder if we'd have to understand it fully to take advantage of it. Would it be possible to make a device that could 'tag' a moment with a unique, potent smell, and thus, reinforce how firmly that moment is committed to memory, and make it easier to bring back in full vivid recollection years later by repeating that scent? Would it be too hit-or-miss, where you couldn't tell which memory-scent-tags would "take" and which wouldn't? Would the intentionality of the act interfere with the process? Are there simply too few strong-but-unique smells they could deliver that way, forcing you to have to choose very carefully when to use it?
Surely, in a world full of desperate venture capitalists and entrepeneurs, along with millions of naïve customers with lots of disposable income and not much discretion, someone must have tried to make and market such a product. If not... quick, let me write up an IPO and someone come make me a millionaire before someone beats me to it.