Short term memory post-it wristwatch?

Often I find that my short term memory fails. For example, when driving to the store I think of something I want to buy. When I get to the store I can't remember it. Or I need to get something from my basement and because I got interrupted on the way I forgot what I wanted. What we need is a simple "wristwatch" device that acts like a simple post-it note with a button to record a couple words (e.g. buy bread), a button to play back the words, and a button to clear the words. The device should hold up to 20 messages. Surely someone is capable of making this. Note that a wristwatch form factor means I don't have to carry my phone and play with an app.