A washer beep is like a webhook: if the recipient fails to acknowledge it, it’s gone forever. A notification is like an /events endpoint: the recipient can catch up on events at their own pace, and be reminded of and see events they haven’t processed.
Half-jokes aside though, I think what we want here is a reminder, i.e. a todo with a timed alert. Beeps can be missed and timers can be stopped (e.g. when you’re occupied), so they aren’t the most fool-proof solution here. Reminders will at least sit in the notifications list until dismissed.