A pager (sometimes called a beeper) is a simple personal telecommunications device for short messages. A one-way numeric pager can only receive a message consisting of a few digits, typically a phone number that the user is then expected to call. Alphanumeric pagers are available, as well as two-way pagers that have the ability to send and receive email , numeric pages, and SMS messages.
Until the popular adoption of mobile phones in the late 1990s, pagers fulfilled the role of common personal and mobile communications. As of 2008, pagers mainly support the "critical messaging" markets. They are the ideal solution for very quick, very reliable personal or group messaging. Unlike most other mobile communications networks, they continue to work in times of emergency or disaster, they do not suffer from network overload as has been proven many times before (9/11, 7/7, Katrina etc.). This is why they are still very popular with emergency service personnel, medical personnel, and information technology support staff.
In the world of paging there are two distinct categories of system in operation. There are on-site paging systems that are used in hospitals to convey the same urgent information as when they were invented in 1956. The other type is wide area paging, which offers similar features as on-site paging, but provides the radio coverage across a city, region or country rather than in just one hospital building.
Originally operating on AM radio frequencies, paging moved to FM schemes prior to becoming a ubiquitous form of communications around the developed and developing world. In some cases, before the advent of cellular phone systems the pager was used as a replacement for a lack of cheap local or international phone services.
Paging is a subscription service offered in a variety of plans and options to meet the needs of a subscriber and the type of device used. In general, all pagers are given unique phone numbers while alphanumeric pagers are given an email address, usually consisting of the phone number.
Upon calling a phone number assigned to a pager, the calling party reaches a recorded greeting asking the caller to enter a numeric message, and sometimes giving the caller an option to leave voice mail. Usually, within a few minutes, the paged person will receive an alert from the pager with the phone number to return the call and/or a pager code. In the case of email paging, the text is displayed.
Most modern paging systems use simulcast delivery by satellite controlled networks. This type of distributed system makes them inherently more reliable than terrestrial based cellular networks for message delivery. Many paging transmitters may overlap a coverage area, while cellular systems are built to fill holes in existing networks. When terrestrial networks go down in an emergency, satellite systems continue to perform. Because of superior building penetration and availability of service in disaster situations, pagers are often used by first responders in emergencies.
Pagers are still in use today in places where mobile phones typically cannot reach users, and also in places where the operation of the radio transmitters contained in mobile phones is problematic or prohibited. One such type of location is a large hospital complex, where cellular coverage is often weak or nonexistent, where radio transmitters are suggested to interfere with sensitive medical equipment and where there is a greater need of assurance for a timely delivery of a message.
Some common environments in which pagers are still used are:
Additionally, some irrigation control systems and traffic signals are now controlled by messages sent via paging networks. Due to energy concerns in the United States and other countries, 2Way paging networks are being used for power company meter reading and control.
Another pager technology in wide use today is the call or tone pager. Mainly used in the hospitality industry, customers are given a theft-protected portable receiver which usually vibrates, flashes or beeps when a table becomes free, or when their meal is ready.
In the United States, pagers typically receive signals using the FLEX protocol in the 900 MHz band. Commercial paging transmitters typically radiate 1000 watts of effective power, resulting in a much wider coverage area per tower than a mobile phone transmitter, which typically radiates around 0.6 Watts per channel.
Although 900 MHz FLEX paging networks tend to have stronger in-building coverage than mobile phone networks, commercial paging service providers will work with large institutions to install repeater equipment in the event that service is not available in needed areas of the subscribing institution's buildings. This is especially critical in hospital settings where emergency staff must be able to reliably receive pages in order to respond to patient needs.
Unlike mobile phones, most one-way pagers do not display any information about whether a signal is being received or about the strength of the received signal. Since one-way pagers do not contain transmitters, one-way paging networks have no way to track whether a message has been successfully delivered to a pager. Because of this, if a one-way pager is turned off or is not receiving a usable signal at the time a message is transmitted, the message will never be received and the sender of the message will not be notified of this fact. In the mid 90's some paging companies began offering a service, which allowed a customer to call their pagernumber, and have numeric messages read back to them. This was useful for time when your pager was off/out of coverage area, as it would know what number paged you even if you never actually received the page.
Other radio bands used for pagers include the 400 MHz band, the VHF band, and the FM commercial broadcast band (88-108 MHz). Other paging protocols used in the VHF, 400 MHz UHF, and 900 MHz bands include POCSAG and ERMES. Pagers using the commercial FM band receive a subcarrier, called the Subsidiary Communications Authority, of a broadcast station.