They are notable for building the very first modern fire engine in 1905, and the first American vehicle with hydraulic brakes, in 1915.

[1] Harry Austin Knox built three experimental gasoline cars at Overman Wheel Company between 1895 and 1898.

[2] The Waltham Watch Company factory was purchased and Knox built 15 cars in their first year.

Rather than flanges to improve the efficiency of cooling, 1,750 threaded 3⁄16 inch (4.8 mm) diameter rods were screwed into the cylinder casing as projecting studs, which led to the engine sometimes being referred to as "Old Porcupine".

A 1904 Knox Tuxedo Touring model, equipped with a straight-twin engine producing 16 hp (12 kW), was priced at $2,200, equivalent to $74,604 in 2023.

[3] In 1906 Knox Automobile Company introduced the Model G, a 40-hp air-cooled four-cylinder engine on a 112-inch wheelbase.

[2] Knox progressively improved their models, moving the engine from under the seat to up front under a hood and going from chain-driven to shaft-drive.