(Police) slang for sirens, because its wailing sound.
That guy was driving so fast I had to hit the wailer.
Wailer---a woman who, in the act of sexual intercourse of any shape and/or form, deems it necessary to moan for an extended period of time, actually making a rather unnecessary ''UUUUUUUUUUUUUUUUH'' sound. If you are experienced enough, you will also know that this can lead to the fabled female orgasm, and for those of us with godlike endowment, the explogasm. This can often frighten away the unfortunate soul who has rounded home with the said wailer, and make him or her disappointingly terrified of intercourse
man that chick last night was a wailer