That's somewhat complex.
The data for a certain product isn't updated on the site, but in the database. It's only shown on the screen if you ask for it via a product identification or via a search.
For new products it's comparable. These are only shown if you search for them or know the product identification they use.
So you need a system that knows what exactly to look for and then grab the html returned by that site if it goes looking for it. And that's the easy case.
In the more difficult case the data is put on the screen using Ajax, and then all a html grabber sees is some javascript and not the data the human reader sees on the screen, because you need a javascript interpreter to find the price.
A price comparator site I happen to know gets an xml from all webshops every day containing all prices. That's much easier to process. But your competitors won't give you that, I suppose.
Kees
I am looking for a online service what can monitor a web site for changes. Specifically trying to find when a competitor updates data on their web site.

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