What type of potentiometer for volume control on 2 C cell battery alarm speaker?

Complete novice here, and I'm trying to figure out what little volume control knob I need to splice into this wire here...

...in order to control the volume of the speaker on this 2 C cell powered alarm device.  This is part of a 2 unit warning system where one box is the motion sensor, and the one pictured is the remote alarm.  When viewed from the outside of the box (through the protective vents), the speaker appears to be made of copper foil.


I have no clue what to look for even if the part was described to me, so would someone please be kind enough to provide a link for a small volume control knob I could splice in that would be appropriate for this application.  Ideally I'd like to drill a small hole and mount it so the knob protrudes through to the outside of the plastic box.


Thanks!
 

Why not use a potentiometer? Isn't that what we usually use to control volume?

Thanks Kevin. Yes that's what I've been told.. to use possibly both a 1k and 10k pot and see if either of those work.