Thanks for the input. Yeah, seems to be difficult to come over any other low cost buzzer than the one with 2 buzzers built-in, one sound. Could be a good solution to hook it up to some LEDs on the model as shown in the video there. If one are further into electronics I guess one could modify and but on some other sounds. But with buzzer sound + LEds blinking it should be easy to detect what model is out of power) It's confusing when we have several models on the track, and it start buzzing