Slightly longer answer turned up a few dead projects of the "Show HN" type if the above isn't right for you and a Chrome plugin from 2017 (https://news.ycombinator.com/item?id=15507334). I know there are a lot of people that use the HN API to scrape for alerts etc so perhaps they have something that they can share. From memory HN doesn't have this feature on purpose to reduce the risk of flame wars erupting.