Whelen GAMMA2 Self Contained Siren Meets SAE Class A sound requirements when used with most 100 watt speakers. Stand-by button provides Hands-Free operation/override from horn ring. Tone button activates Wail tone (may be programmed for other tones). Manual button generates a variety of tones as pre-selected by user, up to 3 tones. Horn button generates an Airhorn tone. Easy to install with standard bail-strap mounting bracket.