This is a little side project of mine. I buy a lot of clothes from ASOS, however often forget to check for a while and end up missing sales. This site will send you an email notification whenever:
* New products launch for a certain search term
* Products within a search term change price
There is also a public listing of price changes [0] (only shows price changes for searches that members are already monitoring). I've already listed several example trackers, including one for the brand 11 Degrees [1]. Email notifications are formatted to include a preview of the product, price, and links to ASOS [2].
It also automatically detected products which have been sold out, and then relisted if more stock comes in, marking them as stale. These products are usually only available in one or two sizes, with very limited stock.
[0] https://asostracker.uk/activity
[1] https://asostracker.uk/trackers/586c1ae510426db2d3c4a817