I pull in real-time stock quotes via DDE, which update every second. I've built a model that looks like the below showing the current Bid and Ask prices, and the difference between the two (aka the "Spread") in col. L. I want to track whenever the Spread for any given row of data is 0.15 or less -- using conditional formatting, I've managed to highlight/outline the cells that meet that condition in yellow font, BUT since Excel is often in the background, I want to create a sound alert for when a spread narrows to 0.15 or less.

The tricky part is that I'd like the sound to play every time the spread drops from above 0.15 to 0.15 or less, but I don't want it to play continuously when the spread is just staying below 0.15...my noob efforts to implement code I've found online have resulted in hearing the beep-alert every second, because the DDE feed is constantly refreshing the data, so I can't just tell the alert to play when cell value =< 0.15. When a spread drops from 0.20 to 0.15 I want an alert...if it stays there or drops further I don't want an alert. But if it later rises to 0.20 and then drops to 0.15 again, I want the alert. aka: I want the alert to play every time the condition goes from an unsatisfied condition to satisfied, but not while it remains satisfied.

spread.jpg