This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The trouble caused by overflowing of the drip pan for an ice box or refrigerator can be overcome by attach- ing a device that will sound an alarm when the water reaches a level safely below the overflow point. A device of this kind may be attached to the back of the refrigerator as shown in the sketch. A float, A, is attached to the lower end of a rod, B, which slides through staples CC. At the upper end of the rod, a V-shaped copper sheet, D, is soldered. This makes the contact points in the electric wiring. The battery E can be placed under or back of the refrigerator as desired. The method of wiring is clearly shown.
Ill: The Float in the Pan, and Contacts for Closing the Circuit to Ring the Bell