Safetran "Hybrid" bells are a very unique type of railroad crossing bell. As their name suggests, they are a cross between mechanical and electronic bells. Mechanical bells have multiple moving parts, whereas the hybrid bell only has one, a tiny striker to ring the gong. Though electronic bells only have speakers and circuit boards, the hybrid bell came before most of them did, making it the most modern bell design.
Hybrid bells came into production in the late 80s or early 90s and remained in production until 2005. They never really caught on with most railroads and can be quite difficult to find. CN used them extensively on their American trackage and used them as well in Canada. KCS, NS, and CSX all used them briefly, but with the exception of Indiana, they have almost disappeared from those railroads. MTS, a light-rail system in San Diego, which is featured in this video, used them extensively, though most are now gone. Today, the highest concentrations of hybrid bells are in Louisiana, Illinois, Indiana, and California.
I am fortunate enough to own a hybrid bell, and I will say, they sure have a unique design. A video of my hybrid bell will be coming out next week, so stay tuned!
