The volunteers carry tone activated pagers. It’s how they get alerted. They are usually a dual tone affair, where two tones are transmitted simultaneously. This helps eliminate false activations of the pager. They are audible because they also alert the firefighter when they are transmitted and open up the muted audible portion of the pager, leaving it open to monitor the initial dispatch information, what type of call, address of call and anything else dispatch needs to convey to the firefighters until the firefighter resets his pager, putting it back in the muted state. (A warbling sound may or may not follow the tones as an attention getter, used in noisy environments (factories) where the alert tones are not sufficient.) Since these audible (analogue) tones are transmitted on the dispatch frequency, there isn’t much to be done about muting them without muting part of the transmission like we can do with the data bursts that precede each transmission of the various apparatus and portable radios. These data bursts are unique to each radio in the field and contain information for the dispatcher such as radio ID (Ex: Engine 2) GPS (location) coordinates which show up on the dispatchers console. The data burst muting feature is adjustable but only up to one second, while the tones to activate a pager can be as long as 8 seconds or more but commonly set for a much less duration.