MRC Steam Sound Sound-only Decoder:
 
The "Sounder" is a sound-only decoder and speaker that's easily added to any HO locomotive equipped with a standard, non-sound decoder or even any piece of rolling stock being pulled by the locomotive equipped with wheel pickups.

Simply "hooks-up" two wires to the track power pickup points in the loco and you can enjoy sound.

The new Steam Sounder reproduces eight genuine articulated and eight non-articulated steam locomotives prime mover sounds and you can select 33 whisles as well.
Use with any HO non-sound decoder from MRC or any other brand
Full 28 NMRA function capability
Select desired sounds and functions in "seconds"
No time consuming downloading or expensive purchases ... all the features are in the decoder
Use with any NMRA compatible DCC system to add sound "on the rails" or "below the rails"
Simple 2-wire hookup
Superb Brilliance sound quailty with multiple sounds and volume selectability
Capable of providing six dynamic lighting effects
18V maximum input
 
MSRP is $49.98.