White Noise Machines for twins

One machine covers a shared twin room, and the shared room is the point: consistent noise is one of the few tools that stops one twin's 3am opinion from becoming both twins' 3am opinion. Put it between the sleep spaces, run it at a safe distance and volume, and treat it as infrastructure.

You only need two when the twins split into separate rooms, and by then you will know exactly which features you use. Skip the app-dependent models that need wifi to make static. Used is fine (it is a speaker in a box), and the travel-sized ones earn their keep the first time you sleep anywhere that is not home.