A warning device which indicates the stoppage of paper in an ink-writing recorder.

A simple and inexpensive warning device is described which indicates when the paper has stopped moving beneath the pens of an inkwriting polygraph. The device operates on the principle that the electrical resistance of the paper under the recorder pen is markedly reduced when the paper stops moving and is made wetter by the ink. A buzzer sounds within a few seconds of the paper stopping and so reduces the possibility of failing to record otherwise irretrievable information, for example during all-night recordings of the EEG in sleep research.