Systems, methods, and techniques for detecting the recording activity of a sensor are described. A monitoring system includes a sensor that is configured to generate sensor data, as well as a failsafe circuit that is configured to monitor an electronic signal of the sensor and determine that the sensor is recording. The system can further include a control unit that receives indication from the failsafe circuit that the sensor is recording and, based on determining that the control unit did not request the sensor to record or that the control unit is not aware that the sensor is recording, the system outputs a signal, e.g. to an indicator light, indicating that the sensor is recording.