PI's favourite audio spy equipment

Shotgun mics are private investigator' s favourite audio spy equipment . Shotgun mic is a type of microphone with a long barrel and a narrow acceptance angle. Shotgun microphones are the most highly directional. They have small lobes of sensitivity to the left, right, and rear but are significantly more sensitive to the front. This results from placing the element inside a tube with slots cut along the side; wave-cancellation eliminates most of the off-axis noise. Shotgun microphones are commonly used on TV and film sets, and for location recording of wildlife, they are also used for audio spying and surveillance.
And here is my favourite
MICRO SMALL SHOTGUN MIC - THE WORLD’S SMALLEST ULTRA-POWERFUL SHOTGUN MIC SYSTEM
The unit is a highly directional soundlocating microphone with an internal high quality amplifier and earphone monitor. High quality miniature 'electret' condenser microphone Supercardiod pick-up pattern. Isolate and pick-up distant sounds. Small,
lightweight and compact; power supply uses a standard UM-4 battery with easy replacement. Sound levels adjustable by volume knob. Mounting hardware for use with binoculars or video cameras. The unit comes with the Micro Supercardiod Mic with built-in Amplifier, wind shield, inner-ear phones and battery.