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An infrared blaster (or IR blaster) is a device that emulates an infrared remote control to autonomously control a device that is normally controlled only by remote control key presses. The most common use of an IR blaster is to allow a recording device such as a DVR or VCR to change the channel on an external tuner such as a cable box or satellite receiver. This way, the recording device can automatically select the correct channel to record before starting the recording process. Another common use is to extend infrared signals in order to place remote controlled products behind closed doors.
Example IR Blaster with standard 1/8" plug
IR Blaster stuck to a cable TV tuner
External links 
Using an IR Blaster with MythTV