On Thursday, Snowden revealed his plan to create an iPhone 6 add-on to keep phones from sending data unexpectedly. He designed it with American hacker Andrew Huang.

Notorious whistle-blower Edward Snowden has helped design an open-source smartphone device that warns people when their phone’s antennae are transmitting information.

The goal is to protect people from being digitally spied on by alerting them when their phone is sending or receiving data without their knowledge or permission.

The device will also feature a ‘kill switch’ so users can quickly cut power if their phone is being tracked; something that the duo says is more secure than airplane mode.

A prototype hasn’t been built as yet, so there’s no evidence it actually works for now, but Snowden and Huang have outlined their design in a paper titled Against the Law: Countering Lawful Abuses of Digital Surveillance.