The SLO-1800 has a unique way of warning an operator if the input or sync signal is missing or has been lost during recording. This smart circuit detects the loss and turns on a WARNING indicator. It is prominently located on the front of the VCR between the VU meters. It shows bright red, it is important and located where will get it attention. It operates two ways. A steady red indicates the VCR doesn't have an incoming signal (which it needs to record anything). This goes away when the signal is restored when it is in the standby mode. The warning light flashes red if the signal is lost during recording. This continues until the signal is restored and another cassette is inserted. Makes sense to have this in a media production facility, and pretty smart.