Federal Signal's Vibratone® heavy duty bell product line utilizes a modular approach to combine gongs and mechanisms allowing for greater flexibility and selection. The Model A4 is four inches in diameter. Each larger gong produces a different tone and a higher dBa output. Vibrating bells produce a continuous ringing sound when voltage is applied. Federal Signal's Vibratone bells can be used in any industrial application, whether to signal danger or for start and dismissal. Vibrating Mechanism is sold separately. 5 Year Limited Warranty.