With regard to audio surveillance, I’ve saved the best for last, if “best” refers to the most devious device on the market. It’s called the “Infinity Transmitter,” and although the technology has been around for decades, the product has only recently been released to the public.
Basically, if you install this transmitter on a target phone, you can then call the number of the target phone from any location. Your call will remotely activate the microphone on the target phone and begin transmitting whatever conversation (or other audible activity) is occurring in the room back to you. In this sense, it’s more of an audio transmitter than a phone tap.
In effect, it transforms a remote phone into a potent bug. And its potency resides in the fact that once planted on the target phone, it can be activated from literally anywhere in the world that can directly dial it.
The device has had a lot of hype in cult circles, with many questioning its existence in the first place. It does exist, but perhaps not on the same all powerful scale that some descriptions afford it. Some of the devices require the target phone to be picked up, at least briefly, then put down again, so repeated one-ringers can get suspicious.
Also when the transmission is in process, some units will render the phone line “busy,” and you can imagine that this will arouse immediate suspicion when a determined caller informs the target that their line has been busy for hours at a time when in reality it has not. Newer models have apparently been designed so as not to require the initial ring to activate the transmitter, but these are not easily available for purchase online. In any case, an Infinity Transmitter will set you back at least $600-$800, and buyers should be warned about the importance of establishing a reliable vendor. Even if this thing is no longer a black market item, it’s still without a doubt in the grey area.