Getting Student Attention in Computer Lab sans Lab Management Software

After reading a discussion about lab management software I began to think about how I have to change a few things now that I no longer have the use of NetSupport in my computer lab. One very specific thought was regarding how to grab the attention of students who are at their computers diligently working during a lesson and wearing headphones. With NetSupport and my wireless mic system I was able to talk to them through their headphones. That was easy. Now, without that capability, I need to come up with something to get their attention that is soemwhat humorous or at least not heavy handed. I'm not fond of the blinking lights method, but may resort to it until I can get some software to do the trick. If anyone has an inexpensive software solution, that would be great.

Thanks,

Charlie