A disconnected computer can emit data in a Wi-Fi frequency band without having a Wi-Fi transmitter. Mordechai Guri demonstrated that channel in AIR-FI, a research paper released in December 2020.
The essential condition comes first: the computer must already be compromised. AIR-FI is a way to move information out of a machine running malicious code. It does not remotely infect a clean computer simply because it is nearby.
The transmitter exploits electromagnetic emissions from memory activity. Instead of sending ordinary network traffic, the program makes the computer's memory buses produce a controlled signal carrying data.
The paper describes reception by nearby Wi-Fi-capable equipment using physical-layer measurements exposed by particular chips. That is different from an ordinary phone automatically receiving a normal Wi-Fi message.
Guri reported data transfer over distances of several meters in the evaluated setups. Performance depends on the transmitting hardware and the receiver. This is a short-range research channel, not a substitute for an internet connection.
The result matters for air-gapped systems, machines deliberately separated from external networks. Removing a network connection addresses one route for data, while the electrical activity of the hardware still exists.
The paper discusses measures including physical separation, monitoring and shielding. Those belong to the specialized threat model being tested. The demonstration's central lesson is narrower than a claim that isolation is useless: disconnected hardware can still radiate.
