Utilization change itself will not generate an alert, but when SW checks the EQ report (once a week, I think) it also scores that day's EQ report. If that results in a score change larger than whatever you have it set for, it's supposed to email you.
Personally, I have credit watch through the Equifax site, which lets me pull Eq every day if I want at no additional charge, and Scorewatch through the MyFICO site.
The FICO site keeps track of my Equifax score, and emails me if it changes and if certain other things happen to the report. It also gives me a single site where I can also pull the score and report from Experian and/or Trans Union if I want to pay for it.
Equifax gives me all the free EQ reports I want, and I often pull one after the FICO Scorewatch tells me about a score change I wasn't expecting.
Also, while Equifax credit watch and FICO Scorewatch are both supposed to tell me about certain changes on my report, and I usually do get emails from both (with FICO always a day later) there have been times when only one of them noticed and told me about something that had changed. So I figure it's worth the extra few bucks to have both.
