The fridge door: the household's shared noticeboard
Reminder cards work because the fridge door is the one surface every person in a home opens, reads, and stands in front of daily. Unlike a drawer or an app, it needs no remembering to consult: a due month pinned there is absorbed in passing, by everyone, including the teenager who will eventually be asked to take the cat in. For an annual obligation that is otherwise invisible for eleven months, that constant low-level exposure is the entire value of the system. The cards must be few, large, and ordered, or the door's clutter swallows them like everything else pinned there.
One card per cat, ordered by what is due next
Use a thick card or a laminated slip per cat, since it must survive a year of handling and fridge humidity without curling into illegibility. Write only four things, big: the cat's name, the due month in the largest hand on the card, the practice name and number, and a blank line for the booked appointment. Pin the stack or row in due order, soonest first, so the card your eye meets first is always the next obligation. A different card colour per cat helps in multi-cat homes, where the risk is less forgetting checkups exist than quietly attributing one cat's completed visit to her housemate.
The booking prompt the card cannot give itself
A card displays a due month but does not count down to it, so build the prompt into your own reading of the door. Agree as a household that when the front card's due month is the next month on the calendar, whoever notices first phones the practice, because routine appointments often need several weeks of lead. Once booked, write the appointment date and time on that card's blank line in a different colour, turning the card from a reminder into a confirmation anyone can check. If the front card sits unbooked into its due month, its plain visibility becomes the nag, which is the system working as designed.
After the visit: rewrite, re-date, and send the card to the back
The discipline step happens the evening of the appointment. Take that cat's card down, note the visit's essentials on its back, weight, vaccines given, anything to recheck, then write a fresh front with next year's due month and pin the card at the back of the order. Moving position is the satisfying signal that this cat is handled for a year, and the new front card instantly becomes the household's next task. Cards that grow crowded with crossings-out should be replaced rather than layered, because a card you have to decode is a card nobody reads while waiting for the kettle.
A card prompts the visit; it cannot document it
For all its visibility, a fridge card holds almost nothing a vet can use, and it stays home when the cat travels. The vaccination history, prior weights, and notes from earlier visits need a home attached to the cat, accessible to whichever family member is at the surgery and producible for boarding or a new practice. Pair the door system with that fuller record rather than asking the card to stretch. Bring KinsLe Pet Passport into the partnership and the card stays the prompt while the passport becomes the proof, carrying this cat's history into rooms the fridge door will never enter.