Postitive supply wire to door bell button. To the 'other side' of the button, connect the buzzer red wire. Connect the buzzer black wire to the negative supply.
i used one of those once as a reverse beeper on my Suburban. as easy as connecting to the reverse light, mounting it below the outside of the tail light, and gluing a piece of plastic wrap over the hole to keep it from filling with water. so, yes, it does work quite well from 12V.