Is there no warning if landing gear is not retracted during flight? I know that most aircraft have a warning system which makes beeping sounds if an aircraft tries to land without the gear down. After reading this news article about an Air India flight 676 flying without retracting the landing gear, I was wondering if there is a reverse mechanism which warns the pilots if the landing gear is not retracted during flight?

If its not there, why?
It's not there because it's like driving with the handbrake on.


  [The flight] was climbing out of Kolkata, however achieved an unusually poor climb rate, was not able to accelerate to normal cruise speeds and leveled off at FL200 after a continuous climb for about 30 minutes (avherald.com).


And because the flight crew should have run the 'after takeoff' checklist, which includes checking that the landing gear is up and locked.

(Source) A typical Airbus A320 checklist.



Related: How much extra drag does landing gear incur?