Not sure what kind of voltage level comes out of the audio line when there is an alert, but you should be able to harness it and turn it into a light. You could put the "audio line out" on the base of a transistor and when there is a voltage increase, it would forward bias that transistor and provide a ground for a light through its collector/emitter. This page shows how to use a transistor as a switch, and if you have someone in your group that's handy with electronics, this could be done in a few hours for less than $5, including case, light, and electronic components.