While hardening a site against surveillance can take many forms, the methods fall into one of two categories. Methods to make device placement more difficult (such as tamper-switches and locks) and methods that make device operation difficult or impossible (such as EMR shielding and powerline filters).
Making instalation of surveillance devices harder can be accomplished
by adding 'tripwires' to common points of access. Typically these access
points can be secured with nothing more than a tamper-proof coating on
the screws that secure them. Removable-strength threadlock (or transparant
nail varnish) would make for a readily noticable anti-tampering system.
The difficulty here is that a well-prepared eavesdropper might have a similar
sealant available, making your counter-tampering tripwire useless. This
can be overcome by adding an ultraviolet-sensitive
powder to the locking substance, making the replacement of your lock
with someone else's readily apparant when illuminated with a blacklight.
Specific areas to apply thread-locking compound to include:
Tamper switches should be installed in as many 'hotspots' as possible.
Any enclosure that houses electronics (phone cabinets, alarm controllers
and control pads, etc) should have a small cherry switch installed, connected
to an alarm circuit. Specific sites to add anti-tamper circuitry include:
Windows are a huge, gaping portal into an area. Aside from providing a staging area for contact microphones and a transmission path for infrared and optical transmitters, people can see you through them. Asthetics aside most area building codes require all rooms to have a window for safety reasons, so boarding them up is out of the question. Add heavy drapes to any windows in the area, using flush curtain rods.
The site's electrical system should have a power-line conditioner installed in order to prevent carrier-current transmissions. If possible any other powered conductors should be filtered. The powerline conditioner should be sealed and inspected regularly, as its possible to bridge across the filter making the conditioning unit an expensive paperweight.
Sites can be hardened against contact and spike microphones by coating the walls (and solid ceiling) with a white-light transparant ultraviolet coating under a transparant protective coating. Under ultraviolet inspection any paint without the UV additive will become immediately obvious.
double glazed windows