This is called Emission leaking which can be picked up by very sensitive sensors from specific distances. It is called
In 1985,
Wim van Eck published the first unclassified technical analysis of the security risks of emanations from
computer monitors. This paper caused some consternation in the security community, which had previously believed that such monitoring was a highly sophisticated attack available only to
governments; van Eck successfully eavesdropped on a real system, at a range of hundreds of
metres, using just $15 worth of equipment plus a
television set.
https://en.wikipedia.org/wiki/Van_Eck_phreaking
Whatever you are typing on your monitor can be picked up by the sensors because when you press a button it emits a electric signal which can be intercepted. Whatever you are Seeing on your crt or lcd monitor can be picked up too because they are emitting electromagnetic emissions which can be picked up by the sensors. This is how FBI snoops on to foreign embassies
http://foreignpolicy.com/2013/11/19/spy-copters-lasers-and-break-in-teams/
Even your sounds or vibrations can be captured by Sensitive sensors and recreate the whole thing
and that is why Emission control (EMCON) and Emission Security (EMSEC) is such a hugh security concern in Military. Whatever you are typing or sending... It can be intercepted so secure your electromagnetic emission
TEMPEST is a
National Security Agency specification and a
NATO certification r
eferring to spying on information systems through leaking emanations, including unintentional radio or electrical signals, sounds, and vibrations.TEMPEST covers both methods to spy upon others and also how to shield equipment against such spying. The protection efforts are also known as emission security (EMSEC), which is a subset of
communications security (COMSEC)
https://en.wikipedia.org/wiki/Tempest_(codename)#Shielding_standards
Radiation intelligence, or
RINT, is
military intelligence gathered and produced from unintentional radiation created as
induction from electrical wiring, usually of computers, data connections and electricity networks
even if you are using laptop then they can see you from cam live at any time even if you are laptop is off !
