"Minesweeper" without a computer

Fluid level indicator comprises a float suspended at the apex by wires from the cover of a fluid reservoir. The float has an upper chamber and a lower chamber separated by an intermediate piece having a concave surface facing the apex. A metal ball in the upper chamber rolls into a depression at the center of the surface to bridge two switch contacts when the fluid level is low and the float is suspended by the wires, which are connected to the contacts. The float is top-heavy and rolls over to open the switch when the fluid level is high enough to permit the suspending portion of the wires to slacken.