The purpose is to send the sound waves into the air to attract swiftlet that may pass the area.
The speakers are waterproof and normally kept indoor at the entry hole.
This special type speaker could help in reduce noise pollution of neighborhood nearby.
The range of distance traveled by the sound produced by speaker is approximate 800 M - 1200 M.

   Long-ranged Sound Speaker System  - USD117.00

(The above price include shipping charge  within Malaysia Only.)