The MIS-07 was designed for the armored vehicle industry to allow the driver to communicate with a person outside, without opening a window. As well as an intercom, the MIS-07 also includes a yelp & wail siren.The MIS-07-11 system consists of a main intercom unit which is mounted under the dash board, a paging horn mounted under the hood and a small microphone which is mounted in the outside rear view mirror on the driver?s side. It includes a hand held microphone with push to talk switch which hangs on a clip mounted on the dash. The MIS-07-21 is exactly the same except it adds a second outside microphone, one for each side of the vehicle. The MIS-07-12 adds a second horn under the hood for double the paging and siren volume. The MIS-07-22 add both of these upgrades. Other custom configurations are also available upon request. Once installed and connected to the vehicle?s 12 volt electrical system, it is ready to use.