These are essentially FM receivers tuned to the same RF frequency as the paging base station in the system. A decoder unit incorpo-rated into each pager will be able to recognize the unique code assigned to the pager and reject all other codes for selective alerting. Pagers can be intentionally assigned the same code for group paging. There are also pagers that can be assigned multiple page codes, typically up to a maximum of four, for individual and group paging and other paging functions. The most basic function of the pager is alerting.
Some pagers are able to perform all three message functions.
Paging systems can be classified into two types manual and automatic paging systems. The page sender uses a standard telephone to call a paging operator and tells the operator who or what number to page. For example, in 2-tone paging format the coded information is two sequential tones having certain frequencies and duration. The operator monitors the paging frequency for traffic. If the channel is free, the operator presses the transmit button to send the pager code and then goes on to the next page.