Low Fuel Light...Possible?

[roll_the_dice]

So I don't really trust my fuel gauge. I ran out once already when the gauge said I had 3/8 of a tank. As I was filling up this morning, I thought of a low fuel light when the tank only had 3 gallons left or so. I was thinking of using the tandem lock indicator on the dash for this light and changing the wording to "fuel reserve" or something. I have used low level sensors and such in fish tanks to signal water topoff, but obviously water isn't combustible...not sure about the sensor triggering a 12v source for the light. Any thoughts??