Signals across the allotments

An original account of an invented allotment signal test.

Before the allotments opened to visitors, the volunteers tested ways of communicating across the site. The paths curved behind sheds and tall hedges, so Priya stood beside the water tank while three volunteers waited at the far gate. She rang a handbell to begin the first test, but its gentle chime could not be heard beyond the greenhouse.

Priya then gave two sharp blasts on a whistle. The volunteers at the gate raised their arms to show that the sound had reached them. To end the test and call everyone back, she beat a wooden spoon against an empty bucket.

What sound told the volunteers that the signal test was over?