To operate the three passive models that do not contain circuitry, the user must supply the entire signal to the alarms. However, innovations incorporated into these alarms by Mallory means that the user needs only to supply a single 325Hz signal to the alarms. The 975Hz fundamental frequency and the harmonic frequencies are generated by acoustic means. In addition to supplying the 325Hz signal, the user must also supply the special timings required to generate the low, medium, and high priority sounds as required by IEC60601-1-8.