Why would I put batteries in that?

Claire and Oliver are having a great time and playing together on this:

But why, why, why, did I put batteries in this:

Yes, it is a siren.  And it sounds just like a police siren.  Not a quiet kids one.  No, no.  It sounds just like the real thing.  Why would I do this?  I have no idea.  What I do know is they better not get hurt because my headphones are up too loud to hear and screaming.