[Heel n Toe]

At wiki:

According to the manufacturer's specifications, the equipment weighs 45 pounds (20 kg) and can emit sound in a 30° beam (only at high frequency, 2.5 kHz) from a device 33 inches (83 cm) in diameter. At maximum level, it can emit a warning tone that is 146 dBSPL (1,000 W/mē) at 1 metre, a level that is capable of permanently damaging hearing, and higher than the normal human threshold of pain (120–140 dB). The maximum usable design range extends to 300 metres. At 300 metres, the warning tone (measured) is less than 90 dB. The warning tone is a high-pitched shrill tone similar to that of a smoke detector.

The luxury cruise ship Seabourn Spirit employed an LRAD while repelling pirates who attacked the vessel with RPGs about 160 km off the coast of Somalia in early November 2005.[6] [7] The effectiveness of this device during the attack is not completely clear, but the pirates did not succeed in boarding the vessel and eventually fled.

The Liberian vessel MV Biscaglia was attacked on November 28, 2008. The security detachment aboard Biscaglia used an LRAD device in an effort to repel attackers armed with assault rifles and rocket-propelled grenades. Following a one-sided shootout, the ship was seized and the unarmed security contractors forced to abandon ship or be killed.[8] The incident caused the usefulness of LRADs to be called into question by Lloyd's List.[9]

http://en.wikipedia.org/wiki/Long_range_acoustic_device