**********Add-on to any 100-200 watt warning siren & Improves emergency vehicle operator safety and siren effectiveness. *****Produces penetrating/vibrating low frequency sound waves able to penetrate vehicles, alerting drivers to your oncoming emergency vehicle. *****Works with any 100/200 watt emergency vehicle siren & Works with any sweeping tone, plus Hi/Low and electronic mechanical tone generated by the primary siren. *****Low Frequency siren sound can be activated via any emergency vehicle steering wheel horn ring. *****Highly effective in dense urban environments with heavy vehicle traffic - 8 second safety timer provides automatic tone shutdown.