"Good Vibrations" was actually recorded using an Electro-Theremin [1] (emphasis mine). It was essentially the same but sported more traditional knob controls. Also if you ever hear a Theremin-esque noise in an Elmer Bernstein soundtrack like "Heavy Metal" it was actually an Ondes Martenot [2] which is distinct from and less similar to the classic Theremin.

I'm a lot of fun at parties.

[1] https://en.m.wikipedia.org/wiki/Electro-Theremin

[2] https://en.m.wikipedia.org/wiki/Ondes_Martenot