So I have had this very simple little gadget idea for years: A "Timestamper Disc"
And i cannot for the life of me understand why it doesn't exist yet. It seems like it would make a perfect kickstarter project.
The Timestamper Disc:
The device would basically be like the watch face of a digital watch -- small, round, thin, powered by watch cell battery.
In its simplest form it would have a single "NOW" button on the front, and would simply display the date and a time that the button was last pressed.
If you had room you might display an additional line showing an natural approximation of the time since the last button push, like "13 days ago" or "6 months ago." If space was tight, you could have the button that cycled through the display of last pushed date, time, approximation, and hold button to trigger the NOW timestamp.
So, what would this device be used for?
You'd want to have several of these around the house -- you could use them to keep track of the last time you changed your water filter, the last time you took your medications, the last time the dog was walked, the last time you called your mother, the last time you used the exercise machine, the last time you cleaned your room, the last time the smoke detector batteries were changed, the last time you ate a snack, the time you woke up, the time you went to sleep, how long ago you put on the last coat of paint, when the lassagne was baked, etc.
You'd just place one of these Timestamping discs on or near the object you want to keep track of (velcro, magnet, band, etc.), and just hit the button when you use the object or perform the task. Now whenever you come back to it, you can see how long it's been since you last performed the event.
They'd be cheap enough that people would buy them in packs of 5 or 10. With watch cell batteries they would last decades. You could probably use watch parts and manufacturing machinery. It's basically a glorified simplified, half-watch.
If you wanted to get fancier, you could put a micro-usb port on it and let users connect to pc/mobile and get historical timestamps of every button press.. And i'm sure you could come up with additional ideas, like being able to set alarms to trigger automatically after the elapse of X amount of time since last press.