STM Products interactive deterrents (DiD 02 model) are selective pingers: the electronics activate on water contact, but ultrasound emission only engages when the system detects dolphins nearby. A built-in listening function recognises the characteristic clicks of cetacean echolocation and, at that moment, triggers the deterrent signal. In the absence of dolphins, the devices remain completely silent. This approach delivers effective protection exactly where it’s needed with a dramatically lower acoustic impact on the marine environment compared to passive models.