It’s impossible for a criminal to tell if a security camera is real or not, so why bother installing real ones?
It may be risky, but using fake cameras saves money and still acts as a deterrent against criminals and vandals.
Obviously you don’t have the protection of a visual recording and real time surveillance. But you also don’t to stay up all night watching the cameras, or pay a security guard to do the job, simply put the fake cameras up and you have 24/7 protection with no running costs.
Saving money on cameras will allow you put the extra funds into the critical, final defences of the security infrastructure. This can be an effective strategy. The criminals who are deterred by the cameras will not approach the property, but the criminals who actually intend to rob the building will have to contend with the increased protection of the critical security systems.