iPhone Keystroke Detection Through ‘Thump Phreaking’ Demonstrated

At Georgia Tech, a team has developed a novel demonstration showing how the accelerometer in an iPhone 4 can function as a keylogger. By simply placing the iPhone next to a computer keyboard, the phone’s accelerometer and gyroscope could interpret typed sentences with up to an 80% accuracy rate.

Previously, similar keylogging methods have been implemented using microphones, which capture vibrations more frequently than accelerometers. However, most mobile operating systems require user consent to access the microphone, which restricts the practicality of such keyloggers.

Currently, mobile applications do not need to request permission to access accelerometers and gyroscopes.

This oversight could potentially allow iPhones and other devices equipped with these sensors to covertly monitor keyboard inputs without the user’s knowledge.

“Imagine downloading a seemingly harmless app, which doesn’t prompt you to enable any suspicious permissions,” explained Henry Carter, a researcher involved in the project. “This app could activate keyboard-detecting malware. The next time your phone is near the keyboard while you type, it could secretly record every keystroke.”

The keylogger operates by recognizing combinations of key presses rather than individual keys, which proved too challenging and inconsistent.

By analyzing these combinations and referencing a pre-established dictionary, the software can accurately identify keystrokes. Our colleague, Mike Rose, has termed this method “thump phreaking,” drawing a parallel to Van Eck phreaking, which involves capturing emissions from CRT or LCD screens to recreate visual data.

It’s important to note that this is merely a proof of concept and not an active threat currently. The researchers acknowledge the complexity of creating this keylogger and its susceptibility to simple countermeasures, such as moving the iPhone just a few inches away from the keyboard.


Linda is a dedicated writer for TUAW, bringing insightful and engaging content to Apple enthusiasts. With a deep understanding of Apple products like the iPhone, iPad, and MacBook, Linda offers readers valuable tips, reviews, and news updates. His articles reflect a genuine love for technology and a commitment to keeping the Apple community informed. Linda’s clear and approachable writing style makes complex topics accessible, ensuring that every reader can stay up-to-date with the latest in the Apple world.