Raspberry Pi Hacking Like Its 1995

PanicAcid's initial tests to send POCSAG messages to a pager
(Image credit: PanicAcid)

Hackers, a 1990s movie that has gained cult status since its release, is well-loved in the hacker and maker communities. Sure its depiction of hacking is a little farcical, but that just adds to its charm ("Rabbit," "flu shot," etc.). The titular hero team of hackers, led by Johnny Lee Miller (Zero Cool) and Angelina Jolie (Acid Burn), communicated via pagers, and modern-day hacker PanicAcid is resurrecting the retro tech with the help of a Raspberry Pi 4.

Some of the best Raspberry Pi projects use retro-tech, and PanicAcid's project is based upon what eBay calls a "Vintage Pager Motorola Advisor." Initially, PanicAcid used a mix of a CH340G USB to serial adapter and DOSBox to run "vintage" software to flash the pager ready for use. After a little more work, PanicAcid could send a page using a HackRF device, but the fun didn't stop there.

Using a combination of a Raspberry Pi 4, software called rpitx, and the Raspberry Pi's GPIO (as well as, crucially, a happy dog), PanicAcid sent a message from the Raspberry Pi to the pager. The protocol to send data to a pager is POCSAG (Post Office Code Standardisation Advisory Group). After learning the unit's frequency and "CAP Code," PanicAcid was all set for the Raspberry Pi part of the hack. 

The rpitx software is a general radio frequency transmitter for Raspberry Pi that doesn't require any other hardware, unless you want to add a bandpass filter to avoid frequencies outside your intended range. The software can handle frequencies from 5 KHz up to 1500 MHz, and a wire attached to GPIO 4 is all you need to act as the antenna for transmission.

Broadcasting an RF signal via the GPIO has been a known trick for some time, and even the Raspberry Pi Pico can transmit over RF. What makes this project special is the protocol and receiving device. Pagers ceased to be a viable messaging system as the popularity of SMS took over. That said, some roles still do use pagers (doctors, surgeons, and system administrators), given their reliability.

This great project from PanicAcid demonstrates that the Raspberry Pi and its GPIO are not just for robotics and blinking LEDs. Of course it would be remiss if we didn't remind you to observe the laws regarding radio transmissions before attempting this project.

Les Pounder

Les Pounder is an associate editor at Tom's Hardware. He is a creative technologist and for seven years has created projects to educate and inspire minds both young and old. He has worked with the Raspberry Pi Foundation to write and deliver their teacher training program "Picademy".