Sanket — "a signal" — works like a traffic light for your prepaid plans. Green while there's time, amber as validity runs low, red just before it ends. You recharge through your own operator, as usual.
AMBER — validity ends this week. Plan your recharge.
Illustrative example
More than a week of validity left.
Seven days or less — time to plan.
Two days or less — recharge with your operator.
Free. Name and email only.