Pagers

by Chris Woodford. Last updated: June 21, 2011.

Beep beep beep! Beep beep beep! Before the days when cellphones started interrupting our lives, there was another form of instant messaging system called paging. Mobile phones have made pagers less popular than they were in the mid-1990s, but paging (or radio paging, to give it its full name) is still a vitally important form of sending messages—especially for doctors and emergency workers. Let's take a look at how it works!

Photo: A modern Motorola Bravo pager. This one has a two-line alphanumeric LCD display and scrolls messages from right to left or up and down, as you prefer. It can either receive pages silently and discreetly, or it can signal a new message by vibrating or beeping. It runs off a small battery that goes in the slot at the bottom.

What is a pager?

Broadcasting (sending instant information to hundreds, thousands, or millions of people at a time) is the big idea that made radio and television so powerful. But what if you want to send a message to only one person? You can certainly send very personal messages over the radio: think how people get their favorite DJs to read "happy birthday" messages out on air. That's instant communication and it works fine if the recipient of the message happens to be listening—but it's a bit hit and miss. And it can be irritating for the other two million listeners who have to "tune out" this irrelevant information that has nothing to do with them!

A pager is a small personal radio receiver that you carry around in your pocket. You have a personal code number or phone number and anyone who wants to send a message to you dials or quotes that number with the message they want to send. That puts them through to a switchboard at a central message broadcasting office, where a person (or more likely a machine) immediately sends out the message with thousands of others, just like a normal radio broadcast, using a network of radio transmitting antennas. All the pagers in people's pockets are constantly picking up all the messages being sent out, but your personal pager ignores any messages that don't contain your personal code. Once a message comes through with your code, your pager buzzes or beeps and displays the message with the date and time.

What is a page?

A page is simply the message or alert sent to or received by a pager and encoded in a burst of radio waves. Back in the 1950s, the first pagers used a crude system called two-tone, in which each pager was designed to respond to a page consisting of two unique sound tones (beeps) sent in rapid succession. If someone paged you, you heard your pager beep twice and you knew someone wanted to talk to you, but not who or why, so you then had to telephone your office or home to find out more. Systems like this could be used to contact a maximum of 870 different pagers, which was fine in those days, when the technology was still very new. By the 1970s, pagers had been improved to use a system called five-six tone, so they responded to a unique code carried in a series of five or six higher-pitched radio frequency tones, with each one lasting 33 milliseconds and an entire page taking about 200 milliseconds (a fifth of a second). Systems like this could support between 100,000 and a million pagers.

Pagers that receive actual messages (rather than simply beeping to alert you) work in a different way, typically using one of two standard page formats (or protocols) called POCSAG or FLEX™. POCSAG (named for the UK's Post Office Code Standardisation Advisory Group, which invented it) can support up to two million pagers and arranges them into a number of different groups that are either "sleeping" (in a battery-saving mode) or "woken up" (ready to receive messages). To send a message to a particular pager with POCSAG, the system first transmits an initial "wakeup" message to activate every pager in the same group and then sends data to them in chunks called frames, with each pager extracting only the messages specifically addressed to it. FLEX™, developed by Motorola, is a newer and much higher-speed paging system that does away with "wakeup" messages by getting pagers to scan for pages at predefined intervals. This makes better use of the airwaves and reduces battery consumption (which means pagers can be made much smaller). According to Motorola, FLEX™ can support over five billion pagers.

Types of paging

There are two different kinds of paging: limited range and wide-area. As the name suggests, limited-range paging sends messages over a relatively small area using a low-powered transmitter. It's perfect for sending emergency messages to all the doctors in a hospital, for example. Wide-area paging is more like national radio broadcasting. A system of radio transmitters sends pager messages across a whole country in hopes that you'll be somewhere near one of them. In the UK, for example, the wide-area paging network uses something like 500 transmitter antennas—more than enough to cover a country that size.

Pros and cons of using a pager

You might think the big disadvantage of paging is obvious: it's a one-way form of communication. If you receive a pager message, you probably have to find a telephone to call back and find out what's going on. But pagers are not really meant to be competing with cellphones: they have a very different purpose—receiving quick, instant messages—and for this they're often much more efficient than phones. Incidentally, two-way pagers (which allow users to indicate that they've received messages) have been widely available since 1995.

What's so good about pagers? One big advantage is that they send messages with VHF (very high frequency) radio signals, typically broadcast in the range 138–466 MHz (similar to normal FM radio programs). Using high-frequency radio means the signals reach further, need fewer transmitters, and suffer less from interfering obstacles than cellphone signals. You're much more likely to receive a pager message in a remote area than a cellphone call or text message, where you may not even pick up a signal. (That's why pagers are often used by mountain rescue teams and lifeboat crews.) Unlike cellphone SMS text messages, wide-area pager messages are typically broadcast and received within 30 seconds. Messages sent over local paging networks, such as those operated by hospitals for their doctors, can be sent and received within five seconds. (Compare that with SMS text messages that can take minutes, hours, or even days to get through if there's congestion on the networks.) It's true that pagers are generally designed for one-way communication, but the lack of a radio transmitter makes them very suitable for environments such as hospitals where mobile phones may be dangerous to use (because their transmitters could interfere with medical equipment).

Who invented the pager?

• 1921: A primitive form of paging is pioneered by the Detroit Police Department, who use radio transmitters to send alerts to squad cars.
• 1949: Canadian inventor Al Gross (1918–2000) invents the first telephone pager. He had already invented the walkie-talkie (in 1938) and Citizen's Band (CB) radio (in 1948).
• 1956: The Motorola electronics company invents the first portable paging device: the Handie-Talkie radio pager. It is soon taken up in hospitals and factories.
• 1974: Motorola introduces the Pageboy I, the first commercially successful pager. It's followed by the even more successful Pageboy II.
• 1981: The UK Post Office introduces a powerful standard format (protocol) for delivering pager messages called POCSAG (Post Office Code Standardisation Advisory Group). Much revised and improved, it remains in use today and can deliver data at rates ranging from 512–2400 bits (binary digits) per second with support for up to two million addresses (unique devices).
• 1986: Motorola develops the Bravo numeric pager. It soon becomes the world's best-selling paging device.
• 1990: The European Union agrees on a Europe-wide paging protocol called ERMES (European Radio MEssage System) with a delivery speed of 6250 bits per second.
• 1993: Motorola announces a powerful new high-speed paging protocol called FLEX™, which can send data at up to 6400 bits per second and support up to five billion addresses (unique devices).
• 1995: Motorola extends FLEX™ into a two-way system called ReFLEX™ and introduces the first two-way pager (the Tango).

Further reading

On this website

• Antennas and transmitters
• Cellphones (Mobile phones)
• Radio
• Telephones
• Television

On other sites

• Paging Protocols by Jay Moskowitz, Real Time Strategies. A very detailed technical introduction comparing how the various paging protocols (such as two-tone, five-six tone, POCSAG and FLEX™) actually work.
• FLEX™ Technology Overview by Motorola. (This is an old, 1998 backgrounder served from the Wayback Machine Internet Archive.)

Books

• Cellular Telephones and Pagers: An Overview by Stephen Gibson. Newnes, 1996.