I've never done it myself but there are a few ways I know of. You can make a piezo sensor similar to a DIY electric kit but instead of triggering sound it lights up a light. Or if you are really on a budget just make a simple circuit between the front of the batter head and your beater so when they touch it lights up. Be careful if doing that way that you don't have live wires sticking about and use batteries not wall power.