HTML tripwire service?

[SamIAm]

Does anybody have a favorite tripwire service? There used to be a couple companies that'd check a given url every morning and email you if the page had changed from yesterday. Sort of like an RSS feed for pages that didn't update very often.

For all I know I made-up the term "tripwire". Or maybe it was the name of one of the companies that did this. I dunno. (This inconsistency makes it hard for me to google for it. [img]/images/graemlins/smile.gif[/img])
-Sam