Spring Reverb?
 

So scouring the local craigslist and I see a Dan Electro Spring King or something. Basically a spring reverb in a pedal.

I want to know, is this a Marketing Gimmick? I guess I dont really know how a real spring unit works on an amplifier, so It could be the same. Just figured Id ask here.

A spring reverb is literally a bunch of springs in a box. It's got a piezo send on one end and a piezo pickup on the other and it runs your signal through there. The Dano unit has I think two little springs. It's not a full sized, "proper" reverb tank like in an amp but it's a decent miniaturized version.

I don't know about the Danelectro, but here's how a spring reverb unit works.

It has a transducer at one end, and a pickup at the other.
The transducer vibrates the springs, and the pickup picks up that vibration, and that gives you your reverb.

Colin, Frank, thank you guys. I appreciate the answers. I have learned something new today.

Oh cool.
The Danelectro has a thing on it to kick the pedal to get that awesome rumbly earthquake sound from hitting the tank.