You can exfiltrate data from air-gapped computer by any means that leaks signals. Some are obvious (wi-fi !?!), fun begins when you use means that aren't normally considered.<p>If I remember correctly (and I'll try to find links afterwards), these were already used:<p>1 - Heat from the CPU/GPU (link: <a href="https://www.wired.com/2015/03/stealing-data-computers-using-heat/" rel="nofollow">https://www.wired.com/2015/03/stealing-data-computers-using-...</a>)<p>2 - Fan noise/speed (link: <a href="https://www.wired.com/2016/06/clever-attack-uses-sound-computers-fan-steal-data/" rel="nofollow">https://www.wired.com/2016/06/clever-attack-uses-sound-compu...</a>)<p>3 - audio from the speaker (link: <a href="http://www.telegraph.co.uk/technology/internet-security/10490846/New-computer-virus-secretly-leaks-data-through-air.html" rel="nofollow">http://www.telegraph.co.uk/technology/internet-security/1049...</a>)<p>4 - audio from the HDD activity (link: <a href="https://www.theregister.co.uk/2016/08/15/air_gap_breached_by_disk_drive_noise/" rel="nofollow">https://www.theregister.co.uk/2016/08/15/air_gap_breached_by...</a>)<p>5 - electromagnetic radiation (<a href="https://www.wired.com/2015/07/researchers-hack-air-gapped-computer-simple-cell-phone/" rel="nofollow">https://www.wired.com/2015/07/researchers-hack-air-gapped-co...</a>)<p>And some ways that I didn't see yet, but might be possible:<p>6 - monitor (by changing part of the screen, the colors, or something like that, creating subtle patterns)<p>7 - keyboard lights (flickering in high speed, perhaps)<p>8 - power consumption<p>edit: added electromagnetic radiation