However, it sometimes also means that bicycles, scooters, and motorcycles stopped at such intersections may be undetected (and therefore risk being ignored by the switch/signal). Most loops can be adjusted manually to consistently detect the presence of scooters and motorcycles at the least. Vehicle classification Inductance loops have also been used to classify types of vehicles. Sampling the loop at a high frequency results in a unique signature for each vehicle allowing for classification of the body type. Metal detector A different sort of "induction loop" is applied to metal detectors, where a large coil, which forms part of a resonant circuit, is effectively "detuned" by the coil's proximity to a conductive object. The detected object may be metallic (metal and cable detection) or conductive/capacitive (stud/cavity detection). Other configurations of this equipment use two or more receiving coils, and the detected object modifies the inductive coupling or alters the phase angle of the voltage induced in the receiving coils relative to the oscillator coil. An anti-submarine indicator loop was a device used to detect submarines and surface vessels using specially designed submerged cables connected to a galvanometer. Audio An audio induction loop, also known as a hearing loop, provides assistance to hearing aid users. The system has one or more loops in the area in which a hearing aid user would be present. Many different configurations can be used depending on the application. Such an induction loop receiver is classically a very small iron-cored inductor (telecoil). The system commonly uses an analog power amplifier matched to the low impedance of the transmission loop. The transmission is normally direct rather than superimposed or modulated upon a carrier, though multi-channel systems have been implemented using modulation. Many hearing aids contain a telecoil which allows the user to receive and hear the magnetic field and remove the normal audio signal provided from the hearing aid microphone site. Since there is no "tuning" available, as the telecoil directly picks up all audio-frequency magnetic fields, careful system design is required where more than one induction loop is used in a building; for example, adjacent movie theatres or lecture halls. Telecoils may also pick up noise from non-audio sources such as power lines, lamps, or CRT monitors. See also Induction coil Inductive sensor Sydney Coordinated Adaptive Traffic System External links Loop and infrared systems - for deaf and hard of hearing people (fact sheet) A practical