These devices are amplified piezo electric crystal accelerometers. Sometimes incorrectly called "contact microphones", or even "electronic stethoscopes". Piezo electric crystals, or elements, generate minute amounts of electrical polarization when placed under direct stress, whereas a microphone converts sound waves into electrical wave forms. Piezo electric crystals accurately measure internal vibrations in a particular plane. In a static situation, where no vibrations are present to cause the element to stress or distort, no electrical polarization occurs.

Once any vibration is detected, the piezo molecules accelerate away from the point of vibration in sympathy with the strength of the vibration or stress, as soon as the vibration is reduced or gone, the molecules return to their static state. If the vibration continues, so the polarization continues, producing a fluctuating electrical output.

Piezo electric crystals may be formed in many ways, and used for many different applications. In this application the crystals are formed into a rod, and the incoming vibrations are detected on one end of the rod, thereby concentrating the vibrations into a small space. This restriction, amplifies the reaction over the full length of the rod, in much the same way that water turns from a steady flow into a strong jet when the exit is constricted. The piezo elements in this product are encapsulated in a metal case which is insulated apart from the case on the top and sides with only the face side having direct contact with the rod. This ensures that the piezo rod reacts to that face FIRST. Owing to manufacturing constraints, and the fact that this device is "operational in the field", it is not practical to isolate some of the extraneous vibrations detected on the other faces of the accelerometer. Therefore, handling by an operator translates into vibrations which makes the rod vibrate which in turn gets amplified along with the target, or desired vibration.

To minimize this adverse effect, the accelerometer has a magnet built into the active face so as to provide "hands free" operation. If a hotel or office wall is the target surface, the included steel screw and flat countersunk washer may be driven into the wall to provide a ferrous surface for the magnet to hold onto. If possible, drive the screw into a stud for the best results. (The stud is connected to both sides of the wall, whereas the sheet rock, or other surface is not.) The vibrations are then concentrated through the screw onto the active surface of the accelerometer.

Internally, the piezo electric polarization's are amplified and then converted to mimic that of a high quality electret microphone.

The COP-ACCLR MKI, is a mono device, whereas the COP-ACCLR MKII is a stereo unit. Both come with a matched, battery operated, small but powerful amplifier that has output connectors for headphones and a tape recorder. A combined on/off volume control allows for necessary adjustments. The MKII has two on/off volume controls, one for each channel, and naturally a stereo output.

The provided amplifiers are designed and filtered with speech recognition in mind. However, the actual accelerometers may be directly plugged into any other high quality sound amp. Also, the frequency response is such that these devices become an excellent tool for deciphering the differing sounds made when the dial of a combination lock is slowly rotated.

The accelerator head is supplied on a 36" cord and measures 30mm in diameter and 18mm in height.