The Adhan for Combining Two Prayers

If the people in a settled area combine two prayers due to rain or similar excuses, is the adhan called for the second prayer, given that people know the time of the second prayer has entered through other means such as the radio?
If they combine—Meaning: in the mosques—two prayers by combining them early, then the adhan is not called for the second prayer; because the obligation of the second prayer has been discharged by knowledge. As for those in the houses, as I said, they can determine the entry of the time by clocks, by the radio, and by observation as well.