Use the technique outlined here: http://www.grangersmithconsulting.com/the-most-undervalued-function-in-qlikview/
HOWEVER - What that blog entry fails to mention is the massive downside to setting thigs to flash on and off every second; becasue you're using the now() and mod() your variable has to be re-calculated by Qlikview EVERY second so can be a massive drain on CPU. This is compounded when you add other parameters to your conditional show; eg when Sales are over X.
I'll never forget the face of a Qliktech employee when I first suggested this a principal few years ago; suffice to say he didn't think it was a good idea.
Matt - Visual Analytics Ltd
New Qlikview Design Blog: http://QVDesign.wordpress.com