In electronics, an opto isolator (or optical isolator, optical coupling device, optocoupler, photocoupler, or photoMOS) is a device that uses a short optical transmission path to transfer an electronic signal between elements of a circuit, typically a transmitter and a receiver, while keeping them electrically isolated since the electrical signal is converted to a light beam, transferred, then converted back to an electrical signal, there is no need for electrical connection between the source and destination circuits. Isolation between input and output is rated at 7500 Volt peak for 1 second for a typical component costing less than 1 US$ in small quantities. The opto isolator is simply a package that contains both an infrared lightemitting diode (LED) and a photodetector such as a photosensitive silicon diode, transistor Darlington pair, or silicon controlled rectifier (SCR). The wave length responses of the two devices are tailored to be as identical as possible to permit the highest measure of coupling possible. Other circuitry for example an output amplifier may be integrated into the package. An opto isolator is usually thought of as a single integrated package, but opto isolation can also be achieved by using separate devices. Digital opto isolators change the state of their output when the input state changes; analog isolators produce an analog signal which reproduces the input.