ActiGraph devices enter a “Low Voltage Mode” (or HALT) state when the battery discharges to 3.1V during normal operation. This mode helps ensure that all accelerometer data is consistent across the discharge profile of the battery by stopping all data collection before the accelerometer reference voltage of 3.0V is reached. In this mode, all important variables are stored in flash memory so as to secure the device download.
Because the device’s internal clock stops in HALT mode, the device cannot be recharged and redeployed. The device must be downloaded and reinitialized to continue use. ActiTrainer devices will display a “HALT” symbol on the OLED display. Other devices will flash the LED three times to indicate the HALT (low voltage) state.