Abstract: A river ice motion detector system for detecting ice run conditions in or to warn communities downstream that flooding from ice jams is possible, comprises a voltage source, a multi-meter, a detector unit and a plurality of sensor loops, all having communication with each other. The voltage source provides an input signal to the detector unit and then to the sensor loops. The sensor loops provides a second signal back to the multi-meter in response to the input signal. The detector unit has a plurality of resistors and a plurality of switches, the values of the resistors determined providing large step differences, allowing the detector unit to determine which of the sensor loops is broken indicating a possible ice run. The switches are normally closed, providing a test for the system when the switches are deliberately opened.