This KA4 Series Keep-Alive(R) device from TCS is used to supply power to decoders during times of power interruption due to dirty track or problematic track work. The KA4 can power a locomotive for 1-2 seconds over dirty track and power interruptions (depending on the number of lights and efficiency of the motor). The result is that if your locomotive loses electrical contact over a long switch frog or a short stretch of dirty track, it′ll keep on running as though the problem didn′t exist. KA4 series Keep-Alive units are sized to fit HO and larger locos. Note: for N Scale and small HO locos check out the KA-N1 Keep-Alive. The KA4 Keep-Alive device is part of the line of Train Control Systems decoders and accessories.WARNING: This product can expose you to chemicals including Lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov