No batteries needed here. Looking back at past technology can not only be fun, but it can help give us a picture of what life was like in the past, as well as let us use their creativity for the future. This creative alarm had a single purpose, to alert you when the door opened. According to the ad, it will "ring violently on slightest pressure". In 1906 this modern technology would of set you back $1, which included shipping and handling (an early variation on Amazon Prime perhaps?).