The fuel gauge that goes to zero in flight WILL get my attention....
Other than that, my watch/timer is my fuel gauge...
Being it is my airplane I know how much I takeoff with and what the
burn rate is... From experience I know that engine surging and tank
switching is normally within five minutes of what my watch calls
for...
Tips are always burned off first then switched with 30 minutes fuel
remaining... This puts me back on the mains and the timer is reset to
put me back on the ground with 30 minutes, or more, left in the
mains... All told an hour of fuel is always left on board and my
personal check list does not allow eating into that reserve for
anything other than a life or death situation... This iron clad rule
is the result of learning the hard way no flameout but the tanks took
exactly the usable amount listed in the POH and has served me well in
the 4 decades since...