with a gas stove, there is a risk that the valve will be opened without a flame being present, allowing for gas buildup which can result in explosion or death from gas inhalation.
to prevent this, a bimetal probe can be suspended in the area of the flame from the burner. this probe will work in the same manner as a pilot light for a water heater. when the flame is present, the valve is kept open. without flame, the valve closes.
to allow for electric starters, when the dial is is the light position, the probe is disconnected from the circuit and gas flows freely. the clicking that is already present as a part of the electric starter will alert the user to the presence of gas flow.-- tcarson, Jun 25 2006random, halfbakery