|Horns for road vehicles are covered by both MoT and Construction and Use regulations. To the best of our knowledge: if your vehicle was manufactured before August 1973 then any "audible" horn is acceptable. If it was manufactured after August 1973 then the horn must be over 40db loud at 1m distant and a "continuous and uniform" (not musical) tone. Therefore for post 73 vehicles you cannot fit a musical horn as the only horn, it would need to be in addition, with a separate activation button, to a standard horn. As a point of reference 116db at source is regarded as the start of the average pain threshold at 1m distant. Most factory issue horns are in the region of 50 to 80db.
All our horns are 12volt only unless an option is given for 6 volt.