HAILERS Main Job: Announcing your boat's presence. Secret Mission: Operating as an audio amplifier. In this capacity, your hailer makes for a good navigator in low visibility. In listen mode, your hailer hears those unseen boats, waves, buoys, and foghorns. Another option? Use your hailer as an extra speaker. Connect it to a VHF, stereo, intercom, another speaker, a security alarm, or a bilge or heat sensor.