Fuel gauge: low fuel indicator

[Mittelklasse]

I got no bar at one time .
Battery was dead. I think that was the sign of the fuel pump not working, the motor couldn't even crank.

On topic: on my Yaris, the last bar starts blinking fast when there's about 12 litres (~3.2 gallons) of gas left.
I once drove for another 100 km (62 miles) and still had about 5 liters left in the tank.

However, I suggest refuelling as soon as possible, as you could potentially burn out your fuel pump driving extendedly with low fuel.
(Gasoline has a cooling effect on the fuel pump.)