radio beacon

But he thought of the invaluable help this radio beacon must be to the mail pilots in the fog.

The strong steady draft guided them like a radio beacon, leading them to their only faint hope of escape and life.

Remember to fly high and follow your radio beacon carefully.

All the while the radio beacon signal was buzzing loudly in his ears.

This tone acts as a radio-beacon, and directs the ants to the colony, no matter where they may be located.