NOISE DETECTION - Detect the source or squeaks, rattles, and other errant or troublesome noises50-FOOT RANGE - Transmitters have a 50-foot signal range allowing use on small and large vehiclesBUILT-IN SPEAKER - Monitor sounds with the built-in speaker or via headphones through the 3.5mm jackSIGNAL STRENGTH INDICATOR - LED lights indicate signal strength of the active channelILLUMINATED CHANNEL BUTTONS - Active channels have illuminated buttons and can be changed or muted with a quick push