Does the cockpit have an alarm to warn about fuel leakage?
In a typical trainer aircraft (in this case, a C172), you have an annunciator panel that includes a &quot;Low Fuel&quot; light:

These lights only come on when fuel is low if the lights are functioning properly. This panel is located prominently, and is easy to notice. This is only one aircraft, but when you consider it is an entry level aircraft that is less sophisticated, it gives a baseline idea of what you could expect to see.
Also, there are fuel gauges displayed with all engine instruments that will indicate accordingly. While this isn't a leak detector, pilots are trained to monitor all instruments regularly and cross check the values - which is how a leak is identified in aircraft with low amounts of technology.
It is worth noting that checking the &quot;LOW FUEL&quot; annunciator is off is a regular checklist item that occurs before you start your actual flight.
As GdD mentions in the comments - you are taught not to rely on any one instrument indication, and panel lights are no exception.