This is a sound trigger for trucks (bogies) on moguls and i got one to modify for use on my ICE train. It is used to activate bell and whistle from sound magnets
It is a terrific thing and it is just so versatile, it was very easy to fit to my ICE train and plugged straight into a 6000 series LGB sound unit in this instance European electric, but will plug into any in that series.
It can be broken down easily to a very small size as well. It is a magnetic reed type switch which is also directional; ie it worked straight away, it will actuate different sounds depending on the relationship to the actuating magnet.
Interestingly as ICE does not have bell and whistle only whistle it gives me an echo in one direction and no echo in another.
Rgds ian