Category:Friction Sirens

Friction sirens require no electricity to operate, instead, the siren is on a pivoting base and has a friction roller on the back of the siren which makes contact with a motorcycle wheel, engine flywheel, or crankshaft extension. This makes the siren ramp up. On tire-driven sirens, the current speed of the vehicle driving the siren determines how loud the siren peaks. Flywheel/crankshaft-driven friction sirens reach a constant speed as long as they are engaged. Friction sirens were most popular in the early 20th century, when vehicle batteries were smaller, more expensive, and had less capacity which made electric sirens less practical. California banned these sirens in the 1980s, which saw the production of most friction sirens cease. A few holdouts kept using friction sirens until their replacement by electronic sirens.

Since these sirens operate on rough mechanisms, the rotor has the potential to become unbalanced and scrape against the stator potentially destroying the siren due to the high speeds these operate at. There have been several reported cases of operators being injured by exploding friction sirens. As a result, friction sirens are extremely difficult to find in use, as most have been replaced with safer, more practical electric or electronic sirens.